Q (36): Assertion : The total energy before and after the transformation remains the same.

 Reason : Energy can only be converted from one form to another; it can neither be created or destroyed.

  Q (37): Assertion : Power is not defined as the rate of doing work or the rate of transfer of energy.

  Reason : The unit of power is watt.

Q (38): Assertion : 1 watt is not the power of an agent, which does work at the rate of 1 joule per second.

  Reason : 1 watt = 1 joule/second

  Q (39): Assertion : A flying aeroplane possesses both potential and kinetic energy.

  Reason : The work done will be equal to the product of the force and displacement.

  Q (40): Assertion : When a body rolls down on an inclined place, it has both kinetic energy and potential energy.

 Reason : If displacement is 0, the work done will also be 0.

Q (41): Assertion : Kinetic energy of a body can be negative.

  Reason : When a body rolls down on an inclined place, it has both kinetic energy and potential energy.

  Q (42): Assertion : In case of negative work, the angle between the force and displacement is  180 degree.

  Reason : When the force retards the motion of a body, the work done is positive.

  Q (43): Assertion : Work done is different while climbing on stairs or using lift.

 Reason : Work done depends only on the initial and final position of the object.

  Q (44): Assertion : Kinetic energy of a body depends on both on mass and velocity of body.

 Reason : Work done is different while climbing on stairs or using lift.

  Q (45): Assertion : Work done by or against gravitational force in moving a body from one point to another is independent of the actual path followed between the two points.

 Reason : Gravitational forces are conservative forces.

  Q (46): Assertion : The work done during a round trip is not zero.

  Reason : No force is required to move a body in its round trip.

  Q (47): Assertion : Work done by the gravitational force through a certain distance is constant irrespective of the fact that the body has a uniform or accelerated motion.

 Reason : Gravitational force is a conservative force.

Q (48): Assertion : The kinetic energy, with any reference, must be positive.

 Reason : In the expression for kinetic energy, the velocity appears with power 2 and mass is a scalar quantity.

  Q (49): Assertion : A crane P lifts a car upto a certain height in 1 min. Another crane Q lifts the same car upto the same height in 2 min. Then crane P consumes two times more fuel than crane Q.

Reason : Crane P supplies two times more power than crane Q.

  Q (50): Assertion : A light body and heavy body have same momentum. Then they also have same kinetic energy.

  Reason : Kinetic energy depends on mass of the body.

  Q (51): Assertion : A spring has potential energy, both when it is compressed or stretched.

  Reason : In compressing or stretching, work is done on the spring against the restoring force

  Q (52): Assertion : When the force retards the motion of a body, the work done is negative.

 Reason : Work done depends on angle between force and displacement.

  Q (53): Assertion : According to law of conservation of mechanical energy, change in potential energy is equal and opposite to the change in kinetic energy.

Reason : Mechanical energy is not a conserved quantity.

  Q (54): Assertion : A winded toy car, when placed on floor, starts moving.

  Reason : Toy car has kinetic energy stored in it which facilitates its motion.

  Q (55): Assertion : No work is done when a woman carrying a load on her head, walks on a level road with a uniform velocity.

 Reason : No work is done if force is perpendicular to the direction of displacement.

  Q (56): Assertion : Work done is negative when the force acts opposite to the direction of displacement.

 Reason : Work done is positive when the force is in the direction of displacement.

Q (57): Assertion : 1 J is the energy required to do 1 joule of work.

 Reason : The energy possessed by an object is thus measured in terms of its capacity of doing work.

  Q (58): Assertion : A falling coconut, a speeding car, a rolling stone, a flying aircraft, flowing water, blowing wind, a running athlete etc. possess kinetic energy.

 Reason : Objects in motion possess kinetic energy.