Physics
Assertion (A) : When a ball is dropped from a height, its kinetic energy decreases and potential energy increases.
Reason (R) : The total mechanical energy remains conserved during the fall, if we ignore air resistance.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true and R is not the correct explanation of A
- Assertion is true but reason is false
- Assertion is false but reason is true
Work, Energy & Power
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Answer
Assertion is false but reason is true
Explanation
Assertion (A) is false because when the ball is released from a height, it falls down and the vertical height of the ball from the ground decreases. Therefore, the potential energy decreases and it changes to kinetic energy due to which the speed of ball increases.
Reason (R) is true because during the fall while transformation of mechanical energy from one form to the other desired form, some part of it changes to other undesirable form usually heat due to the presence of air resistance but when air resistance is absent then no losses occur and hence the total mechanical energy remains conserved.
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Related Questions
1 kWh is equal to :
- 746 Н.Р.
- 3.6 x 10-6 J
- 3.6 Ј
- 3.6 x 106 J
Assertion (A) : The power spent in doing a work remains the same, even if the same work is done in a lesser time.
Reason (R) : The power spent by a source depends on the time taken by the source to do that work.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true and R is not the correct explanation of A
- Assertion is true but reason is false
- Assertion is false but reason is true
Fill in the blanks:
(a) Work is said to be done by a force only when …………… .
(b) Work done = Force x …………… .
(c) The energy of a body is its capacity to do …………… .
(d) The S.I. unit of energy is …………… .
(e) The potential energy of a body is due to its …………… and kinetic energy of a body is due to its …………… .
(f) Gravitational potential energy U = mass x force of gravity on unit mass x …………… .
(g) Kinetic energy = x mass x …………… .
(h) Power P = …………… / time taken.
(i) The S.I. unit of power is …………… .
(j) 1 H.P. = …………… W.
Write true or false for each statement:
(a) A coolie does no work against the force of gravity while carrying a luggage on a plane road.
(b) The energy stored in water of a dam is kinetic energy.
(c) The energy of a flying kite is kinetic energy.
(d) Work done by a boy depends on the time in which he does work.
(e) Power spent by a body depends on the time for which it does work.