Question

. A 70 kg person is riding on a frictionless skateboard at 5 m/s. A friend facing him throws a 5 kg ball toward him at 20 m/s. What is his final speed after catching the ball

Answer 1

Answer on Question 48988, Physics, Mechanics — Kinematics — Dynamics A 70 kg person is riding on a frictionless skateboard at 5 m/s. A friend facing him throws a 5 kg ball toward him at 20 m/s. What is his final speed after catching the ball?

Solution

Momentum conservation law is

$m_{person}v_{person}+m_{ball}v_{ball}=(m_{person}+m_{ball})v$

where v is final velocity. So we have

$v=\frac{m_{person}v_{person}+m_{ball}v_{ball}}{m_{person}+m_{ball}}=\frac{70\cdot 5+5\cdot(-20)}{5+75}=3.125\,m/s$

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