Question

20 kg who is running at a speed of 4.0 m/s jumps onto a stationary sled of mass 5.0 kg on a frozen lake. the speed at which the child and sled begin to slide across the ice is most nearly

Answer 1

Here we can use momentum conservation as there is no external force on sled and child while he jump on sled

by momentum conservation equation

$m_1v_{1i} + m_2v_{2i} = m_1v_{1f} + m_2v{2f}$

$20*4 + 5*0 = 20*v + 5 *v$

since sled and child both moves with same speed so here they both will have same final speed "v"

by solving above equation we will have

25 v = 80

v = 3.2 m/s

So they will move together with speed 3.2 m/s