Question

A car of mass 500 kg is moving at 10 m / s. The engine does work on the car and the speed increases to 16 m / s.

How much work is done by the engine to increase the speed of the car?

(A) 3000 J (B) 9000 J (C) 39 000J (D) 78 000J

THESE ARE THE OPTIONS TO CHOOSE FROM

AN ANSWER WOULD BE APPRECIATED!!!

Answer 1

Answer:

Initial speed u=36 km/h=10 m/s

Final speed v=72 km/h=20 m/s

Now change in KE=

2mv 2− 2mu 2change in KE=

2500×20 2 − 2

500×10

2ΔKE=7.5×10

4 J

Answer 2

Answer:

F=u

dt

dm

+m

dt

du

=u

dt

dm

since u is constant.

∴F=10m/s×10kg/min=10×

60

10

kgm/s

2

=

3

5

N