Question

Two adjacent students stand on stationary skateboards, face each other, and push apart. The skateboarder on the left weighs 65 kg, the one on the right is 85 kg. If the lighter skateboarder moves at 3.2 m/s, determine the speed and direction of the heavier skateboarder.

Answer 1

As we know that two skateboarder will push each other so there is no external force on this system

Hence we can use momentum conservation here

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

$0 + 0 = (65)(3.2) + 85(v)$

now we have

$0 = 208 + 85 v$

$v = - 2.45 m/s$

so the heavy skateboarder will move off with speed 2.45 m/s in the opposite direction