A car of mass 400 kg and travelling at 72 km h^(-1) crashes into a truck of mass 4000 kg and travelling at 9 km h^(-1) in the same direction. The car bounces back at a speed of 18 km h^(-1). The speed of the truck after the impact is

A car of mass 400 kg and travelling at 72 km h^(-1) crashes into a tru

1.	A car of mass 400 kg and travelling at 72 km h^(-1) crashes into a truck of mass 4000 kg and travelling at 9 km h^(-1) in the same direction. The car bounces back at a speed of 18 km h^(-1). The speed of the truck after the impact is
Answer» `9 km h^(-1)` `18 km h^(-1)` `27 km h^(-1)` `36 km h^(-1)` Solution :Here, `m_1 = 400 KG, m_2 = 4000 kg ` `u_1 = 72 km h^(-1) = 72 xx 5/18 ms^(-1) = 20 ms^(-1)` `u_2 = 9 km h^(-1) = 9 xx 5/18 = 2.5 ms^(-1)` `v_1 = -18 km h^(-1) = -18 xx 5/18 = -5 ms^(-1)` `v_2 = ?` ACCORDING to law of conservation of LINEAR momentum , we get `m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2v_2` `400 xx 20 + 4000 xx 2.5 = 400 xx (-5) + 4000 xx v_2` `20 + 25 = 5 + 10v_2` `45= 5 + 10v_2` `v_2= 5MS^(-1) = 5 xx 18/5 km h^(-1) = 18 km h^(-1)`.