Q7 The marking scheme states that let v be the velocity of A at immediately after the impact, means the impact time=0, momentum is conserved.
We just need to calculate the instantaneous momentum(velocity)
Puppet's explanation is correct
20# 包包 klau1001
分離是瞬時的 除非題目寫明0.01 s之類
ok, i just move back to my original question
Why conservation of momentum cannot be used in Q7 (except horizontal consideration) ?
本帖最後由 aildux 於 4-4-2009 19:11 編輯
The ball A only moving horizontally(left side), so the horizontal momentum is conserved.
However, the vertical velocity of the ball A is zero after the collision.
It seems the ball B collide with the ground(only consider the vertical component), so that vertical momentum is not conserved.(the fixed point provides an external force such as the ground provides an external force)