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# mech question watch

1. Hi i am on the last question of my hw and i am stuck and i was wondering if anyone could help me on it

Q8) A ball is thrown vertically upwards with a speed of 15 ms-1 from a point 1m above the ground. Find the speed with which it hits the floor .If it rebounds with a speed which is half the speed with which it hits the floor, find its greatest height after the first bounce.

I am completely stumped here could ANYONE help me on this question
2. For part a)

Use:

And then for part b)

Use: to find s, the highest height (eg. the height when velocity = 0)
3. v^2=u^2+2as
We start at s=0, so the height of the ground is -1.
The initial speed, u, is 15, and the acceleration is -g (take upwards as positive).
So v=sqrt(15^2 - 2g(-1)).
Your answer will depend on g, usually we take g=10, 9.8 or 9.81.
Let the rebound speed be w, so w=0.5v.
At the greatest height, the velocity will be momentarily zero (think about it).
So using the same formula:
0^2 = w^2 -2gh
So h=(w^2)/2g
4. cheers guys u really helped me out thanks for the help its gr8ly appreciated

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