Answer:
The change in length per unit length per degree rise in temperature of copper is 0.000017k
Explanation:
Given that :
The linear expansivity of copper is 0.000017k. This simply means that ; for a given copper length, the length of such copper will increase by 0.000017k for every degree rose in temperature of the copper rod.
Therefore, the change in length per unit length per degree rise in temperature (k) is 0.000017
Good conductors have:
Question 9 options:
A) current moves easily
B) conserves energy-easy for electrons to move
C) all of the above
D) low resistance
Answer:
[tex]\boxed{\boxed{\sf all \ of \ the \ above }}[/tex]
MORE TO KNOW Materials that easily allow the current to pass through it are called Good conductor Materials that can pass the current but not as much as good conductor are called poor conductor Materials that did not allow the current to pass through are called Insulator Current is produced when a group of electrons move through a conductor SI unit of Current is Ampere Ammeter is an instrument that measures Electric current SI unit of charge is Coulomb ( equal to 6 × 10 power 18 electrons )The electric difference between the points make electrons move This difference is called Potential differenceIt is measure by an instrument called VoltmeterGood conductors have: current moves easily, low resistance, conserves energy-easy for electrons to move. Hence, Option (C) is correct.
What is conductor?Materials that easily permit the flow of electricity are referred to be electrical conductors. Conductivity is the quality of conductors that enables them to conduct electricity.
Electric current is the name given to the movement of electrons through conductor. Voltage is the amount of power necessary to cause that current to flow through the conductor.
Such an element receives a charge that is dispersed along its entire surface, causing the electrons inside the element to migrate. Charges are transferred to an electrical conductor, and they disperse until the minimal force of repulsion between electrons in locations of excess electrons. Such an item transfers its charge to another conductor when it comes into contact with it, reducing the overall repulsion caused by charge in the process.
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Secretariat is known as the horse with the fastest run in the Kentucky Derby. If Secretariat's record 1.25 mi run lasted 1 minute 59.2 seconds, what was his average speed in m/s
Answer:
v = 16.87 m/s
Explanation:
Given that,
Distance, d = 1.25 miles
d = 2011.68 m
Time, t = 1 minute 59.2 seconds
= 60 s + 59.2 s
= 119.2 s
We need to find the average speed of the horse. It is given by total distance covered divided by total time.
[tex]v=\dfrac{2011.68 \ m}{119.2\ s}\\\\=16.87\ m/s[/tex]
So, his average speed is 16.87 m/s.
Consider a star that is a sphere with a radius of 6.32 108 m and an average surface temperature of 5350 K. Determine the amount by which the star's thermal radiation increases the entropy of the entire universe each second. Assume that the star is a perfect blackbody, and that the average temperature of the rest of the universe is 2.73 K. Do not consider the thermal radiation absorbed by the star from the rest of the universe. J/K
Answer:
The value is [tex]\Delta s = 8.537 *10^{25 } \ J/K[/tex]
Explanation:
From the we are told that
The radius of the sphere is [tex]r = 6.32 *10^{8} \ m[/tex]
The temperature is [tex]T_x = 5350 \ K[/tex]
The average temperature of the rest of the universe is [tex]T_r = 2.73 \ K[/tex]
Generally the change in entropy of the entire universe per second is mathematically represented as
[tex]\Delta s = s_r - s_x[/tex]
Here [tex]s_r[/tex] is the entropy of the rest of the universe which is mathematically represented as
[tex]s_r = \frac{Q}{T_r}[/tex]
Here Q is the quantity of heat radiated by the star which is mathematically represented as
[tex]Q = 4 \pi * r^2 * \sigma * T^4_x[/tex]
Here [tex]\sigma[/tex] is the Stefan-Boltzmann constant with value
[tex]\sigma = 5.67 * 10^{-8 }W\cdot m^{-2} \cdot K^{-4}.[/tex]
=> [tex]Q = 4 \pi * (6.32*10^{8})^2 * 5.67 * 10^{-8 } * 5350 ^4[/tex]
=> [tex]Q = 2.332 *10^{26} \ J[/tex]
So
[tex]s_r = \frac{2.332 *10^{26}}{2.73}[/tex]
=> [tex]s_r = 8.5415 *10^{25}\ J/K[/tex]
Here [tex]s_x[/tex] is the entropy of the rest of the universe which is mathematically represented as
[tex]s_x = \frac{Q}{T_x}[/tex]
=> [tex]s_x = \frac{2.332 *10^{26} }{5350}[/tex]
=> [tex]s_x = 4.359 *10^{22} \ J/K[/tex]
So
[tex]\Delta s = 8.5415 *10^{25} - 4.359 *10^{22}[/tex]
=> [tex]\Delta s = 8.537 *10^{25 } \ J/K[/tex]
This question involves the concepts of entropy and the thermal radiation
The entropy of the entire universe is increased by "8.41 x 10²⁵ J/k
".
The increase in entropy is given as follows:
[tex]\Delta s = s-s_T[/tex]
where,
Δs = increase in entropy = ?
σ = Stefan-Boltzman's constant = 5.67 x 10⁻⁸ W/m².k⁴
A = surface area = 4πr² = 4π(6.32 x 10⁸ m)² = 5.01 x 10¹⁸ m²
Tr = Absolute temperature of the star = 5350 K
T = absolute temperature of the rest of the universe = 2.73 k
Q = thermal radiation energy
Q = [tex]\sigma A T_r^4=(5.67\ x\ ^{-8}\ W/m^2.k^4)(5.01\ x\ ^{18}\ m^2)(5350\ k)^4=2.3\ x\ 10^{26}\ J[/tex]
s = entropy of the universe = [tex]\frac{Q}{T}=\frac{2.3\ x\ 10^{26}\ J}{2.73 k}=8.42\ x\ 10^{25}\ J/k[/tex]
[tex]s_T[/tex] = entropy of the star = [tex]\frac{Q}{T_r}=\frac{2.3\ x\ 10^{26}\ J}{5350\ k}=4.3\ x\ 10^{22}\ J/k[/tex]
Therefore,
Δs = 8.42 x 10²⁵ J/k - 4.3 x 10²² J/k
Δs = 8.41 x 10²⁵ J/k
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Can I get help on this question please I don’t understand
Answer:
A
Explanation:
Weight = 55 * 9.8 = 539 N
Scale = 686 N
Since the scale reading is larger than the lady’s weight, the elevator must be accelerating as it moves upward.
Net upward force = 686 – 539 = 147 N
147 = 55 * a
a = 147 ÷ 55
The acceleration is approximately 2.67 m/s^2.
How do the permanent magnets in an electric generator induce a current in a loop of wire that is moving between them?
A. The magnets cause charged particles within the wire to move as the poles of the magnets switch.
B. The moving electrons flow from the permanent magnets into the loop of wire.
C. The magnetic field of each magnet attracts the metal in the moving loop of wire.
D. The magnetic field between the magnets causes the charged particles within the wire to move.
Correct answer is D
The magnetic field between the magnets causes the charged particles within the wire to move.
According Faraday's law of electromagnetic induction, whenever their is a relative motion of a conductor is magnetic field, an emf will be induced in the conductor and the strength of the induced emf is directly proportional to the rate of change of magnetic flux linking the circuit.
The motion of the electrons is due to magnetic field created by the permanent magnet of the electric generator.
Thus, the magnetic field between the magnets causes the charged particles within the wire to move.
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Which statement accurately describes thermal energy?
Answer:
here are the options.
Answer:
the energy that is associated with temperature or D
Explanation:
Hope this helps
A 0.60-kg mass at the end of a spring vibrates 3.0 times per second with and amplitude of 0.13m. Determine
(a) The velocity when it passes the equilibrium point,
(b) The velocity when it is 0.10 m from equilibrium
(c) The total energy of the system, and
(d) The equation describing the motion of the mass, assuming the x was a maximum at t = 0.
Answer:
a) The velocity when it passes the equilibrium point is [tex]\pm 2.451[/tex] meters per second.
b) The velocity when it is 0.10 meters from equilibrium is [tex]\pm 1.567[/tex] meters per second.
c) The total energy of the system is 1.802 joules.
d) The equation describing the motion of the mass, assuming that initial position is a maximum is [tex]x(t) = 0.13\cdot \sin (18.850\cdot t +0.5\pi)[/tex].
Explanation:
a) If all non-conservative forces can be neglected and spring has no mass, then the mass-spring system exhibits a simple harmonic motion (SHM). The kinematic formula for the position of the system ([tex]x(t)[/tex]), measured in meters, is:
[tex]x(t) = A\cdot \sin(\omega \cdot t +\phi)[/tex] (1)
Where:
[tex]A[/tex] - Amplitude, measured in meters.
[tex]\omega[/tex] - Angular frequency, measured in radians per second.
[tex]t[/tex] - Time, measured in seconds.
[tex]\phi[/tex] - Phase, measured in radians.
The kinematic equation for the velocity formula of the system ([tex]v(t)[/tex]), measured in meters per second, is derived from (1) by deriving it in time:
[tex]v(t) = \omega\cdot A\cdot \cos (\omega\cdot t+\phi)[/tex] (2)
The velocity when it passes the equilibrium point occurs when the cosine function is equal to 1 or -1. Then, that velocity is determined by following formula:
[tex]v = \pm \omega\cdot A[/tex] (3)
The angular frequency is calculated by this expression:
[tex]\omega = 2\pi\cdot f[/tex] (4)
Where [tex]f[/tex] is the frequency, measured in hertz.
If we know that [tex]f = 3\,hz[/tex] and [tex]A = 0.13\,m[/tex], then the velocity when it passes the equilibrium point, which is the maximum and minimum velocities of the mass:
[tex]\omega = 2\pi\cdot (3\,hz)[/tex]
[tex]\omega \approx 18.850\,\frac{rad}{s}[/tex]
[tex]v = \pm \left(18.850\,\frac{rad}{s} \right)\cdot (0.13\,m)[/tex]
[tex]v = \pm 2.451\,\frac{m}{s}[/tex]
The velocity when it passes the equilibrium point is [tex]\pm 2.451[/tex] meters per second.
b) First, we need to determine the spring constant of the system ([tex]k[/tex]), measured in newtons per meter, in terms of the angular frequency ([tex]\omega[/tex]), measured in radians per second, and mass ([tex]m[/tex]), measured in kilograms. That is:
[tex]k = \omega^{2}\cdot m[/tex] (5)
If we know that [tex]\omega \approx 18.850\,\frac{rad}{s}[/tex] and [tex]m = 0.60\,kg[/tex], then the spring constant is:
[tex]k = \left(18.850\,\frac{rad}{s} \right)^{2}\cdot (0.60\,kg)[/tex]
[tex]k = 213.194\,\frac{N}{m}[/tex]
Lastly, we determine the velocity when the mass is 0.10 meters from equilibrium by the Principle of Energy Conservation:
[tex]U_{k} + K = K_{max}[/tex] (6)
[tex]\frac{1}{2}\cdot k\cdot x^{2} + \frac{1}{2}\cdot m\cdot v^{2} = \frac{1}{2}\cdot m\cdot v_{max}^{2}[/tex] (7)
Where:
[tex]U_{k}[/tex] - Current elastic potential energy, measured in joules.
[tex]K[/tex] - Current translational kinetic energy, measured in joules.
[tex]K_{max}[/tex] - Maximum translational kinetic energy, measured in joules.
[tex]v[/tex] - Current velocity of the system, measured in meters per second.
[tex]m[/tex] - Mass, measured in kilograms.
[tex]v_{max}[/tex] - Maximum velocity of the system, measured in meters per second.
If we know that [tex]k = 213.194\,\frac{N}{m}[/tex], [tex]x = 0.10\,m[/tex], [tex]m = 0.60\,kg[/tex] and [tex]v_{max} = \pm 2.451\,\frac{m}{s}[/tex], then the velocity of the mass-spring system is:
[tex]\frac{k}{m} \cdot x^{2} + v^{2} = v_{max}^{2}[/tex]
[tex]v^{2} = v_{max}^{2}-\frac{k}{m}\cdot x^{2}[/tex]
[tex]v = \sqrt{v_{max}^{2}-\frac{k\cdot x^{2}}{m} }[/tex] (8)
[tex]v = \sqrt{\left(\pm 2.451\,\frac{m}{s} \right)^{2}-\frac{\left(213.194\,\frac{N}{m} \right)\cdot (0.10\,m)^{2}}{0.60\,kg} }[/tex]
[tex]v \approx \pm 1.567\,\frac{m}{s}[/tex]
The velocity when it is 0.10 meters from equilibrium is [tex]\pm 1.567[/tex] meters per second.
c) The total energy of the system ([tex]E[/tex]), measured in joules, can be determined by the following expression derived from the Principle of Energy Conservation:
[tex]E = \frac{1}{2}\cdot m\cdot v_{max}^{2}[/tex] (9)
If we know that [tex]m = 0.60\,kg[/tex] and [tex]v_{max} = \pm 2.451\,\frac{m}{s}[/tex], then the total energy of the system is:
[tex]E = \frac{1}{2}\cdot (0.60\,kg)\cdot \left(\pm 2.451\,\frac{m}{s}\right)^{2}[/tex]
[tex]E = 1.802\,J[/tex]
The total energy of the system is 1.802 joules.
d) Given that initial position of the mass-spring system is a maximum, then we conclude that the equation of motion has the following parameters: ([tex]A = 0.13\,m[/tex], [tex]\omega \approx 18.850\,\frac{rad}{s}[/tex] and [tex]\phi = 0.5\pi\,rad[/tex])
From (1) we obtain the resulting formula:
[tex]x(t) = 0.13\cdot \sin (18.850\cdot t +0.5\pi)[/tex] (10)
The equation describing the motion of the mass, assuming that initial position is a maximum is [tex]x(t) = 0.13\cdot \sin (18.850\cdot t +0.5\pi)[/tex].
B. How does potential energy change when
mass is increased?
Answer:
with the increase in mass of the object , the force of gravitation increases that eventually increases the potential energy if the object is still fixed in its relative position with surrounding objects.
Explanation:
hopes this will help you
help plz i need it in the next 30 mins
Answer:
i think it's d
Explanation:
Answer:
D
Explanation:
i feel like this one is it
Define a rotation of the earth answer fast
Answer:
here u go
Explanation:
Earth's rotation is the rotation of planet Earth around its own axis. Earth rotates eastward, in prograde motion. As viewed from the north pole star Polaris, Earth turns counterclockwise.
PLEASE HELP! what kind of electricity does electrical heat burners make
Answer:
Electrical to Thermal
2. Two identical spheres having charges Q and -
2Q experience a force F at a certain distance
If the spheres are kept in contact and then
placed at same initial distance, the force
between them will be
force between the two charges (+q1 and +q2),if they are at a distance 'a' is
F1=1/4pieEo q1q2/d^2................ (1)
when the metal spheres are in contact the charge flow from one sphere to another till both the sides acquires the same charge. here q1 and q2 are of same sign,hence after contact each sphere will have a charge
[tex] \binom{q1 + q2 }{2} [/tex]
now,the force between them,
f2=1/4pieEo
(q1+q2/2)^2/d^2
from eq (1)and eq (2)
f2=f1 (q1+q2)^2/4q1q2
The wave produced by a piano's middle C has a frequency of 440 Hz
and a wavespeed of 344 m/s. What is its wavelength?
Answer:
0.78 m
Explanation:
I just did a hw question for this its just 344 divided by 440
Parent: My son spends three hours on homework every night. He has no time to see his friends. He has no time to relax. We are watching him turn into a homework machine instead of a human being.
Answer:
this is a homework helping website I don't know If I can help you with this problwm
Can you help with this question please
Answer:
First answer to the first question is Two people pulling a rope with the same force in a opposite direction. The other one would be 2.72N
Explanation:
Hope this helps you :)
A little girl is walking, swinging her arms through a 20° angle every 0.25 s. The length of each arm is 30 cm. Assuming that the arms move with constant speed during each swing, find the force that the blood vessel in her arm would exert on a 1-gram drop of blood from the end of the arm if her arm were not swinging.
Answer:
The force will be "[tex]9.8\times 10^{-3} \ N[/tex]".
Explanation:
The given values are:
Mass,
m = 1 gram
Angle,
Ф = 20°
As we know,
⇒ [tex]F=mg[/tex]
On substituting the given values in the above expression, we get
⇒ [tex]=(1.0\times 10^{-3})(9.8)[/tex]
⇒ [tex]=9.8\times 10^{-3} \ N[/tex]
why is it difficult to lift out the bucket form well
because of gravitional pull
Can hurricanes produce tornadoes
Answer:
No
Explanation:
Answer:
No
Explanation:
Tornadoes are usally produced in the Midwest regions. Hurricanes are made with water, not clouds. So, no, hurricanes cannot produce tornadoes.
Using a light microscope, a student identified the following characteristics of four organisms found in a sample of pond water. Based on the observations of the student,
which organisms most likely belong to the taxonomic group for bacteria?
Pond-Water Organisms
Organism 1 Single-celled, nucleus, large vacuole
Organism 2 Single-celled, no nucleus, cell wall
Organism 3 Single-celled, no nucleus
Organism 4 Single-celled, nucleus
Organism 1 and 4
Organism 1 and 2
Organism 3 and 4
Organism 2 and 3
Answer:
Organisms 2 and 3
Explanation:
Using a scale of 1 cm to represent 10 N, find the size and direction of the resultant of forces of 50 N
and 30 N acting at the angle of 45 O to each other.
Answer:
[tex]74.31\ \text{N}[/tex]
[tex]16.59^{\circ}[/tex]
Explanation:
P = 50 N
Q = 30 N
[tex]\theta[/tex] = Angle between the vectors = [tex]45^{\circ}[/tex]
Resultant is given by
[tex]R=\sqrt{P^2+Q^2+2PQ\cos\theta}\\\Rightarrow R=\sqrt{50^2+30^2+2\times 50\times 30\times \cos45^{\circ}}\\\Rightarrow R=74.31\ \text{N}[/tex]
Angle of resultant
[tex]\phi=\tan^{-1}\dfrac{Q\sin\theta}{P+Q\cos\theta}\\\Rightarrow \phi=\tan^{-1}\dfrac{30\times \sin45^{\circ}}{50+30\cos45^{\circ}}\\\Rightarrow \phi=16.59^{\circ}[/tex]
Magnitude of the resultant is [tex]74.31\ \text{N}[/tex]
Direction of the resultant is [tex]16.59^{\circ}[/tex]
an effort force 40n is applied to a screwdriver to pry the lid off of a can of pain. the screwdriver applies 100n of force to the lid. what is the MA of the screwdriver?
Answer:
MA = 2.5
Explanation:
Given that,
Effort force applied to a screwdriver to pry the lid off of a can= 40 N
The screwdriver applies 100n of force to the lid = 100 N
We need to find the mechanical advantage of the screwdriver. Mechanical advantage of a machine is given by the ratio of load to the effort.
m = load/effort
= 100/40
= 2.5
Hence, the MA of the screwdriver is 2.5
A force of 100 N acts on a body and moves at a distance of 2 m in the direction of the force. How much work has been done?
Answer:
200 joules
Explanation:
work=force×distance
Can cause a stationary object to start moving or moving object to change its speed or direction or both
Answer:
Force
Explanation:
Only a force can cause a stationary object to move or a moving object to change its speed or direction.
Water can form large dewdrops in nature how would droplets made of vegetable oil instead of water be different
Answer:d
Explanation: oil would form droplets but only tiny ones because it’s surface tension is lower than that of water
Both water and vegetable oil would made droplets but Oil would form only very tiny droplets because its surface tension is lower than that of water.
What is surface tension?Surface tension is the propensity for liquid surfaces that are at rest to condense into the smallest surface area. Razor blades and insects (like water striders), which have a higher density than water, can float on the surface of the water without even becoming partially buried because to surface tension.
Surface tension at liquid-air contacts originates from the liquid molecules' stronger attraction to one another due to cohesion than to the air molecules (due to adhesion).
As the surface tension of the oil is lower than that of water, it forms droplets will smaller size.
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a machine
of efficiency of 70% is used to raise
a body of
mass 80 kg through
a vertical distance of 3m in
40 seconds. Calculate the power input. (Take g = 10 m/s²)
Answer:
Power_input = 85.71 [W]
Explanation:
To be able to solve this problem we must first find the work done. Work is defined as the product of force by distance.
[tex]W = F*d[/tex]
where:
W = work [J] (units of Joules)
F = force [N] (units of Newton)
d = distance [m]
We need to bear in mind that the force can be calculated by multiplying the mass by the gravity acceleration.
Now replacing:
[tex]W = (80*10)*3\\W = 2400 [J][/tex]
Power is defined as the work done over a certain time. In this way by means of the following formula, we can calculate the required power.
[tex]P=\frac{W}{t}[/tex]
where:
P = power [W] (units of watts)
W = work [J]
t = time = 40 [s]
[tex]P = 2400/40\\P = 60 [W][/tex]
The calculated power is the required power. Now as we have the efficiency of the machine, we can calculate the power that is introduced, to be able to do that work.
[tex]Effic=0.7\\Effic=P_{required}/P_{introduced}\\P_{introduced}=60/0.7\\P_{introduced}=85.71[W][/tex]
2) Two railway tracks are parallel to west east direction. Along one track, train A moves with a speed of 45 m/s from
west to east, while along the second track, train B moves with a speed of 60 m/s from east to west calculate speed of
Bw.rt. A
Answer:
[tex]Relative\ Velocity = 105m/s[/tex]
Explanation:
Given
[tex]V_A = 45m/s[/tex]
[tex]V_B = 60m/s[/tex]
Required
Determine the speed of B w.r.t A
The question implies that, we determine the relative velocity of B w.r.t A
Because both trains are moving towards one another, the required velocity is a [tex]sum\ of\ velocities\ of[/tex] both trains:
This is shown below:
[tex]Relative\ Velocity = V_A + V_B[/tex]
[tex]Relative\ Velocity = 45m/s + 60m/s[/tex]
[tex]Relative\ Velocity = 105m/s[/tex]
Number 1a and b and number 2(everything)
Answer:
Explanation:
The density of a substance is the ratio of its mass to its volume. Its unit of measurement is kg[tex]m^{-3}[/tex].
i.e density, ρ = [tex]\frac{mass}{volume}[/tex]
1a. To determine the density of the acetic acid, Rachael needs to know the mass and volume of the acid.
i. Measure the mass of the given beaker using the mass balance.
ii. Transfer the acetic acid into the beaker, and measure the new mass using the mass balance.
iii. Subtract the mass of the beaker from the new mass to determine the mass of the acetic acid.
iv. Measure the volume of the acid on the scale of the beaker.
v. Divide the value of the mass by its volume to determine its density of the acetic acid.
b. Given that the density is 1.05 g/[tex]cm^{3}[/tex], and volume is 200 [tex]cm^{3}[/tex].
Then,
density = [tex]\frac{mass}{volume}[/tex]
1.05 = [tex]\frac{mass}{200}[/tex]
mass = 1.05 x 200
= 210 g
mass = 210 g
2. Length of titanium = 0.40 m
Area of titanium = 0.05 [tex]m^{2}[/tex]
mass = 90.0 kg
density = [tex]\frac{mass}{volume}[/tex]
But,
volume = area x length
= 0.05 x 0.4
= 0.02 [tex]m^{3}[/tex]
density of titanium = [tex]\frac{90}{0.02}[/tex]
= 4500 kg[tex]m^{-3}[/tex]
A has a frequency of 300 Hz and a wavelength of 1.10 m. What is the velocity of the wave?
Hello!!
For calculate the Velocity of the wave let's applicate the formula:
[tex]\boxed{V=f*\lambda}[/tex]
[tex]\textbf{Being:}[/tex]
[tex]\sqrt{}[/tex] V = Velocity = ?
[tex]\sqrt{}[/tex] f = Frequency = 300 Hz
[tex]\sqrt{}[/tex] [tex]\lambda[/tex] = Wavelength = 1,1 m
⇒ [tex]\text{Then let's \textbf{replace it according} we information:}[/tex]
[tex]V = 300 \ Hz * 1,1 \ m[/tex]
⇒ [tex]\text{Let's resolve it: }[/tex]
[tex]V = 330 \ m / s[/tex]
[tex]\textbf{Result:}\\\text{The velocity is \textbf{330 meters per second}}[/tex]
Answer:
For calculate the Velocity of the wave let's applicate the formula:
V = Velocity = ?
f = Frequency = 300 Hz
= Wavelength = 1,1 m
⇒
⇒
Explanation:
how is red shift evidence of the big bang
it implies our universe is expanding
it implies our universe is collapsing
it implies our universe is standing still
Answer:
it implies our universe is expanding
A fruit bat falls from the roof of a cave. We know that her potential energy was
600 J, and that the roof of the cave was 12.8 meters high. What is her velocity
when she hits the ground?
Answer:
v = 15.65 m/s
Explanation:
We use conservation of mechanical energy between initial (i) and final (f) states:
Pi + KEi = Pf + KEf
At the top of the cave at the instant the bat starts to fall, there is only potential energy since the bat's velocity is zero.
Pi = m g h = 600 J
and the KEi = 0 J (no velocity)
Knowing the height of the cave's roof (12.8 m) , we can find the mass of the bat:
m = 600 J / (g 12.5) = 4.9 kg
Using conservation of mechanical energy, the final state is:
Pf + KEf = 600 J
with Pf = 0 (just touching the ground)
KEf= 1/2 4.9 (v^2)
and we solve for the velocity:
600 J = 0 + 1/2 4.9 (v^2)
v^2 = 600 * 2 / 4.9 = 244.9
v = 15.65 m/s