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# Mechanics 1 - Velocity-Time graph help. watch

1. Hi guys,

I'm having some trouble on part (d) of this M1 question. I have looked at the mark scheme (attached if you need it) but still do not get it!

I understand that if you take downward motion to be positive that the graph initially increases, but why does the graph then drop below 0 when the particle hits the ground? Can someone also explain the subsequent stages of the graph as well?

Would really appreciate it because I am quite confused!
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2. (Original post by DhylanP - CRGS)
Hi guys,

I'm having some trouble on part (d) of this M1 question. I have looked at the mark scheme (attached if you need it) but still do not get it!

I understand that if you take downward motion to be positive that the graph initially increases, but why does the graph then drop below 0 when the particle hits the ground? Can someone also explain the subsequent stages of the graph as well?

Would really appreciate it because I am quite confused!
Velocity (note, not speed), is intially zero, and as the ball falls becomes postive and increasing, and then it hits the ground, and the ball's direction and velocity are reversed (it's bounced), it's now suddenly negative, speeding in the opposite direction - upwards. As it goes up, it slows down, and the velocity becomes less negative until at the maximum height it is zero. It then starts to fall again and the velocity is now positive and increasing.

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Updated: February 12, 2018
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