The kick!
A football, if it was kicked when initially at rest, is inflated such that it will move in the direction of the kick with of the kicking foot's velocity.
We now consider the same ball being kicked while it's moving towards the football player's foot. Before the kick the ball moves towards the soccer player with velocity and the player kicks the ball in the opposite direction with foot velocity .
What is the ball's speed after the kick in m/s ?
Details and assumptions
- All speeds in this problem (including the answer) should be with respect to the ground.
The answer is 22.
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1 solution
Let's go to the frame that has the velocity equal to that of the ball before the kick. In that frame, the foot's velocity is v + u and the ball stays at rest, so we know what happens: the ball's final velocity is h ( v + u ) = 1 2 m/s . In the frame at rest with respect to the ground, the velocity is therefore h ( v + u ) − v = 2 m/s .