Answer to Question #288385 in Physics for Junard

Question

A 2500 kg delivery truck contains 125 cavans of rice, each of mass 500 kg. Its moving at a speed of 5m/s. How many cavans of rice must be unloaded at a nearby grocery so that the track can move at 9m/s and yet maintain the same momentum( Identify the given, unknown and equation to use.)

Answer 1

Initial momentum:

$$p_i=(M+N_1m)v_i,\\ p_f=(M+N_fm)v_f,\\ p_i=p_f,\\\space\\ (M+N_1m)v_i=(M+N_fm)v_f,\\\space\\ N_f=\dfrac{(M+N_1m)v_i-Mv_f}{mv_f}=71,\\\space\\ \Delta N=N_i-N_f=54.$$