1. A force can do no work on a body, yet the body can move under accelerated motion.
a) True
b) False
Explanation: When the force is perpendicular to the direction of motion, the force can do no work on a body even if it is under accelerated motion. The moon revolves around the earth under the centripetal force of attraction of the earth, but the earth does not work on the moon.
2. What sort of energy does flying bird posses?
a) Potential energy
b) Kinetic energy
c) Elastic energy
d) Both potential and kinetic energy
Explanation: A flying bird possesses both kinetic and potential energies because it is at a certain height above the ground and moving with a certain velocity.
3. When a spring is compressed or stretched, the potential energy of the spring ___________
a) Decreases
b) Stays constant
c) Increases
d) Becomes zero
Explanation: The potential energy of a spring increases when it is compressed or stretched because work is done on it when it is compressed or stretched.
4. The water at the foot of the fall will be at a different temperature from that at the top.
a) True
b) False
Explanation: When water falls from a height, its potential energy is converted into kinetic energy and its velocity is maximum at the foot of the fall. The velocity is suddenly reduced to zero, and hence its kinetic energy gets converted into heat energy raising its temperature.
5. When the momentum of a body is doubled, its kinetic energy ___________
a) Remains the same
b) Drops to zero
c) Becomes four times its initial kinetic energy
d) Becomes ten times its kinetic energy
Explanation: K = 1/2 mv2 = (mv)2/2 m = p2/2 m
K α p2
When the momentum of a body is doubled, its kinetic energy becomes four times the initial kinetic energy.
6. When the velocity of an aeroplane is doubled, the momentum ___________
a) Remains unchanged
b) Is conserved
c) Becomes zero
d) Increases uniformly
Explanation: If velocity of the aeroplane is doubled, its momentum is also doubled. However, combined momentum of air and aeroplane is conserved. As the momentum of aeroplane increases, the momentum of air also increases by an equal amount in the opposite direction.
7. What happens to the potential energy when one proton and one electron are brought close together?
a) The potential energy gets increased
b) The potential energy gets converted into kinetic energy
c) The potential energy gets remains the same
d) The potential energy gets decreased
Explanation: The potential energy gets decreased when a proton and an electron are brought close because the work is done by the force of attraction between them.
8. In a thermal power station, coal is used for the generation of electricity. How energy changes from one form to another before it is transformed into electrical energy?
a) Heat energy->Mechanical energy->Electrical energy
b) Heat energy->Electrical energy->Mechanical energy
c) Mechanical energy->Heat energy->Electrical energy
d) Electrical energy->Heat energy->Mechanical energy
Explanation: The heat energy produced due to combustion of coal converts water into steam. The heat energy of steam is converted into mechanical energy when it turns blades of a turbine. The mechanical energy so obtained is converted into electrical energy by the generators.
9. A metal ball rebounds better than a rubber ball.
a) True
b) False
Explanation: When a rubber ball hits a massive object, it is distorted. A large amount of heat is generated in the ball by the rubbing of the rubber molecules against each other. This effect is essentially absent in hard material. So, a metal ball would lose less energy upon collision than would a rubber ball.
10. A cylinder rolls up an inclined plane, reaches some height and then rolls down (without slipping throughout these motions). The direction of the frictionless force acting on the cylinders is ___________
a) Up the incline, while ascending and down the incline, while descending
b) Up the incline, while ascending as well as descending
c) Down the incline, while ascending and up the incline, while descending
d) Down the incline, while ascending as well as descending
Explanation: Whether the cylinder rolled up or down, the centre of mass and hence the point of contact of the cylinder has an acceleration g sinθ in the downward direction. Hence in both cases, the force of friction acts up the inclined plane.