question_answer

A car of mass m is driven with acceleration a along a straight level road against a constant external resistive force F. When the velocity of car is v, the rate at which the engine of the car is doing work will be

A)  Fv                         

B)  mav    

C)  (F+ma)v                             

D)  (ma-f)v

Correct Answer: C

Solution :

Let \[{{F}_{e}}\] is the constant force exerted by engine then \[{{F}_{e}}-F=ma\Rightarrow {{F}_{e}}=F+ma\] Power i.e. the rate at which engine is doing work is, \[P={{F}_{e}}v=(F+ma)v\]