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  • An automobile engine propels a 1000 kg car (A) along a levelled road at a speed of 36 km h–1. Find the power if the opposing frictional force is 100 N.

An automobile engine propels a 1000 kg car (A) along a levelled road at a speed of 36 km h–1. Find the power if the opposing frictional force is 100 N. Now, suppose after travelling a distance of 200 m, this car collides with another stationary car (B) of same mass and comes to rest. Let its engine also stop at the same time. Now car (B) starts moving on the same level road without getting its engine started. Find the speed of the car (B) just afte the collision. 

Answers (1)

Solution.
Mass of the car = 1000 kg
Speed of car A    = 36 km/h = 10 m/s
Frictional force =100 N
We know that power is defined as:
Power = Fv
Hence, power of engine will be:
 Power = (100N) (10m/s) =1000 watt.
In the collision, no external force is involved. Therefore, total momentum of both cars will be conserved.
m_{A}u_{A}+m_{B}u_{B}=m_{A}v_{A}+m_{B}v_{B}
Where m_{A}=1000kg;m_{B}=1000kg;u_{A}=10m/s;u_{B}=0m/s;v_{A}=0m/s;

By putting the values, we will get:
v_{B}=10m/s;

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