1. A bullet of mass 20g is found to pass two points 30m apart in a time interval of 4s. Calculate the kinetic energy of the bullet if it moves with constant speed.
a) 2.5J
b) 5J
c) 0.562J
d) 2J
Explanation: Speed, v = (Distacne )/Time = 7.5m/s
Kinetic energy = 1/2×0.02×7.52 = 0.5625J.
2. Potential energy is also called mutual energy.
a) True
b) False
Explanation: Potential energy is also called mutual energy. It is measured by the amount of work that body or system can do in passing from its present position to some standard position, called zero position.
3. The kinetic energy is water is used to run turbines.
a) True
b) False
Explanation: The potential energy of water stored to great heights in dams is used to run turbines for generating hydroelectricity.
4. What energy does a stretched bow posses?
a) Kinetic energy
b) Gravitational energy
c) Elastic potential energy
d) Potential energy
Explanation: A stretched bow possesses potential energy. As soon as it is released, it shoots the arrow in the forward direction with large velocity. The potential energy of the stretched bow gets converted into kinetic energy.
5. Which of the following is not a conservative force?
a) Elastic force
b) Gravitational force
c) Force of friction
d) Electrostatic force
Explanation: A force is conservative if the work done by the force in moving the particle around any closed path is zero. Therefore, force of fiction is the non conservative force.
6. Calculate the velocity of the bob of a simple pendulum at its mean position if it is able to rise to a vertical height of 10cm. Take g = 9.8m/s2
a) 5m/s
b) 1.5m/s
c) 14m/s
d) 1.4m/s
Explanation: By conservation of energy,
Kinetic energy of the bob at the mean position = Potential energy of the bob at the highest position
That is, 1/2mv2=mgh
v = √2gh = √(2×9.8×0.10) = 1.4m/s.
7. How high must the body be lifted to gain an amount of potential energy equal to the kinetic energy it has when moving at a speed of 20m/s? g=9.8m/s2
a) 20m
b) 20.0m
c) 202m
d) 22m
Explanation: mgh = 1/2mv2
h = v2/2g = 20.2m.
8. A ball is thrown vertically upwards with a velocity of 20m/s. At what height, will its kinetic energy be half its original value?
a) 10.20m
b) 10m
c) 15m
d) 5m
Explanation: Work done against gravitation = Change in kinetic energy
mgh = 1/2 mv2-1/2×1/2 mv2
h = v2/4g= 10.20m.
9. The total energy of the universe is constant.
a) True
b) False
Explanation: As the entire universe may be regarded as an isolated system, the total energy of the universe is constant. If one part of the universe loses energy, another part must gain an equal amount of energy.
10. How much mass is converted into energy per day in Tarapur nuclear power plant operated at 107 kW?
a) 10g
b) 9g
c) 9.6g
d) 2g
Explanation: Power, P = 107 kW = 1010J/s
Time, t=1day=24×60×60s
Energy produced per day, E = Pt = 864×1012J
E = mc2
m = E/c2 = 9.6g.