1. Answer : (c) remains constant
Explanation: Since, the total energy of the system is always conserved, so when a body falls freely towards the earth, then its total energy remains constant i.e.the sum of the potential energy and kinetic energy of the body would be the same at all points.
2. Answer : (a) acceleration
Explanation: When both spheres are dropped simultaneously from a tower, then they have same acceleration because during free-fall acceleration of the body becomes equals to acceleration due to gravity. The acceleration due to gravity depends on mass of earth and the radius of earth. Hence, The acceleration will be same.
3. Answer : (d) initial velocity of the object
Explanation: Here, F= force applied on the object, d= displacement, and 0 is the angle between force and displacement. So, the work done on an object does not depend upon the initial velocity of the object.
4. Answer : (a) \(36\times10^5\;J\)
Explanation: One kilowatt-hour is equivalent to the energy of 1,000 joules used for 3,600 seconds or 3.6 million Joules. In equation form: 1 kWh = 3.6 million J.
5. Answer : (a) 4 times
Explanation: The change in the kinetic energy of the object as the speed changes is proportional to the square of the factor by which the speed changes. For example, if the speed of the object becomes double, its kinetic energy changes to four times the initial kinetic energy.
6. Answer : (b) a force of 1 N displaces a body by 1 m
Explanation: 1 Joule is the amount of work done when a force of 1 Newton displaces a body through a distance of 1m in the direction of the force applied.
7. Answer : (c) kinetic energy and potential energy
Explanation: Mechanical Energy of a body includes both kinetic energy and potential energy.
8. Answer : (a) Power
Explanation: power is the rate of doing work. It is the amount of energy consumed per unit of time.
9. Answer : (d) 0
Explanation: Work done by a centripetal force is always zero as centripetal force always act perpendicular to the direction of motion.
10. Answer : (a) power is more
If work is done faster, power is higher. If work is done slower, power is smaller.
11. Answer : (c) zero
Explanation: The moon is revolving around the earth. In this process, the work done by the gravitational force is zero because the displacement of the moon is at the right angle to the gravitational force.
12. Answer : (d) mechanical energy
Explanation: The energy possessed by an oscillating pendulum of a clock is the sum of potential energy and kinetic energy and this sum is known as mechanical energy.
13. Answer : (a) 9 times
Explanation: The Kinetic Energy is increased by a factor of 9 if the velocity is tripled.
14.Answer : (a) Energy
Explanation: A body at rest can have energy, i.e. potential energy, or momentum. Energy is the ability to do work. The Law of conservation of energy: Energy can neither be created nor be destroyed, only Energy can be converted from one form to another.
15. Answer : (c) Both potential and kinetic energy
Explanation: An airplane flying has both kinetic and potential energy because it is in motion due to which it has kinetic energy and it is flying at some height from the earth's surface due to which it has potential energy also.
16. Answer : (a) Speed
Explanation: If the speed of an object is doubled by increasing its velocity, its kinetic energy becomes four times its initial value. Thus kinetic energy increases by four times when its momentum is doubled. Hence kinetic energy of a body is increased most by doubling its speed.
17. Answer : (a) heat caused by the force of friction
Explanation: That warmth is caused by a force called friction. When objects like your hands come in contact and move against each other, they produce friction. Friction happens when you overcome the resistance of one object rubbing against the other. Rub them together and there's friction.
18. Answer : (d) KW h (kilowatt-hour)
Explanation: The energy used in households, industries, and commercial establishments are usually expressed in kilowatt hour 1 kWh.
19. Answer : (d) Work done
Explanation: The area under the force-displacement curve represents the work done. It is the distance (s) of the object displaced by the application of the force (f).
20. Answer : (d) he is standing on the roof
Explanation: Potential energy is the multiplication of mass, acceleration due to gravity and height of the object. So, the maximum potential energy at height. Hence, The person will have maximum potential energy when he is standing on roof.