Question

Some kid (mass 20 kg) jumps with a velocity of 3.2 m/s horizontally off some steps (height 0.55 m) onto his heavy duty skateboard (mass 3 kg, height 0.03 m), which is initially at rest. How fast will he be skating?

Answer 1

Need to find initial momentum and final momentum. So, initial momentum is mass of kid times their velocity plus the mass of skateboard times its initial velocity(vi=0). Therefore, Pi=(20)(3.2)+(3)(0). Final momentum equals the mass of the kid times its final velocity (which is unknown) plus the mass of skateboard times its final velocity (also unknown). So, Pf=(20+3)vf. Solve for vf by setting Pi equal to Pf due to momentum conservation. (20)(3.2)+(3)(0)=(20+3)vf. Final velocity turns out to be 2.783 m/s