Question

A car changes its speed from $20km{h}^{-1}$ to $50km{h}^{-1}$. This is possible only if _________ is applied on the car.

Answer 1

Newton's second law of motion:

1. According to Newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place in the direction of the force.
2. If a greater force is applied, a greater change in velocity takes place, and hence, there will be a greater change in momentum.
3. Here the car changes its speed from $20km{h}^{-1}$ to $50km{h}^{-1}$.
4. Thus, to increase the momentum an external force is applied to the car, thereby changing its speed.