Physics Multiple Choice Questions on “Potential Energy”.
1. The potential energy of an object maximises as its velocity increases.
a) True
b) False
Answer: b
Clarification: The potential velocity of an object is maximum when it is at rest. The kinetic energy increases as velocity increases while the potential energy decreases.
2. An object of mass 5kg is taken from a height of 10 m to a height of 30 m. What is the increment in its potential energy? (Assume g = 10m/s2)
a) 500 J
b) 1000 J
c) 1500 J
d) 2000 J
Answer: b
Clarification: PE = m x g x h
m = 5 kg
g = 10 m/s2
Let;
h1 = 10m
h2 = 30m
PE1 = 5 x 10 x 10
= 500 J
PE2 = 5 x 10 x 30
= 1500 J
Increment in PE = PE2 – PE1
= 1500 – 500
= 1000 J.
3. A 10kg object is raised to a height of 20m. What is the magnitude of its potential energy? (Assume g = 10 m/s2)
a) 500 J
b) 1000 J
c) 1500 J
d) 2000 J
Answer: d
Clarification: PE = m x g x h
m = 10 kg
g = 10 m/s2
h = 20 m
PE = 10 x 10 x 20
= 2000 J.
4. An object is thrown from the ground with a velocity of 5 m/s. If the object has a mass of 2kg, what will be its potential energy at the top-most point of its trajectory? (Assume g = 10 m/s2)
a) 5 J
b) 15 J
c) 25 J
d) 50 J
Answer: c
Clarification: Maximum height reached by the object;
h = v2/(2 x g)
= 25/20
= 1.25 m
PE = m x g x h
= 2 x 10 x 1.25
= 25 J.
5. Which of the following is true?
a) Potential energy decreases as altitude increases
b) Potential energy increases as altitude increases
c) Potential energy first increases and then decreases as altitude increases
d) Potential energy first decreases and then increases as altitude increases
Answer: b
Clarification: As altitude increases potential energy increases. From the equation of potential energy (PE);
PE = m x g x h
We can see that the potential energy is directly proportional to height. Hence the statement is justified.
6. Since the potential energy of an object depends on the acceleration due to gravity and since the acceleration due to gravity decreases as altitude increases, we can conclude that the potential energy of an object decreases as altitude increases.
a) True
b) False
Answer: b
Clarification: The potential energy of an object does not depend on acceleration due to gravity at the instantaneous position of the object but depends on the acceleration due to gravity at the reference point (such as the surface of the earth). Hence, potential energy increases as altitude increases.
7. Consider 2 balls A and B of the same mass. The potential energy of ball A is thrice that of ball B. How high is ball A compared to ball B?
a) Same height as ball B
b) Twice as high height as ball B
c) Thrice as high height as ball B
d) Four times as high height as ball B
Answer: c
Clarification: PEa = (m x g x h) a
PEb = (m x g x h) b
ma = mb = m
ga = gb = g
PEa = 3 x PEb
ma x ga x ha = mb x gb x hb x 3
m x g x ha = m x g x hb x 3
ha = 3 x hb.
8. The potential energy of an object of constant mass and fixed reference is determined by its _____
a) mass
b) gravitational acceleration
c) position
d) velocity
Answer: c
Clarification: PE = m x g x h
The mass of the given object is constant.
The fixed reference indicates constant acceleration due to gravity.
Hence, variation in height (h) is nothing but a variation in position.
Hence, the potential energy of an object of constant mass and fixed reference is determined by its position.
9. The potential energy of an object cannot be increased by internal forces.
a) True
b) False
Answer: a
Clarification: The potential energy can only be increased by external forces. Energy increase by internal forces manifests as an increase in kinetic energy. However, potential energy can be reduced by internal forces by increasing kinetic energy.
10. Find the ratio of potential energy if an object is raised to thrice of its height and its mass is tripled.
a) 1:1
b) 1:4
c) 1:9
d) 1:3
Answer: c
Clarification: PE1 = m x g x h
PE2 = (3m) x g x (3h)
= 9 x m x g x h
PE1 : PE2 = mgh : 9mgh
= 1:9.