Question

A car of mass 1000 kg moving witha velocity of 90 km/h collides with a tree and comes to stop in 10 s. What is the change in momentum of the car? What is the force applied by the tree to stop the car?

Answer 1

The change in momentum of the car

$$\Delta p=m|v_f-v_i|$$

$$=1000\: \rm kg\times |0\: m/s-90\: \frac{1000\: m}{3600\: s}|=25000\: kg\cdot m/s$$

The force applied by the tree to stop the car is equal

$$F=\frac{\Delta p}{\Delta t}=\rm\frac{25000\: kg\cdot m/s}{10\: s}=2500\: N$$