2002 · Q39
Assertion (A)A bus and a car (with lower weight than that of the bus) moving at the same velocity, are brought to rest on a level road by applying brakes which exert same retarding force. The car will travel lesser distance before coming to rest.
Reason (R)The kinetic energy to be destroyed is equal to the work done by the retarding force.
Select the correct answer using the codes given below:
General SciencePhysics
- ABoth A and R are true and R is the correct explanation of A
- BBoth A and R are true but R is NOT the correct explanation of A
- CA is true but R is false
- DA is false but R is true
Explanation
Both the bus and the car move at the same velocity, so the heavier bus has the greater kinetic energy (½mv²). The same retarding force F must do work F·s equal to that kinetic energy, so the bus needs a longer stopping distance s — the lighter car stops sooner, making the assertion true. The reason correctly states the work–energy principle (work done = kinetic energy destroyed), which is exactly why the car stops in the shorter distance. Both are true and R explains A — option (A).