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# mechanics question - will give rep. watch

1. can't do this dam question although im sure its not too difficult.

tennis ball his so that it moves vertically downwards from a height of 1m with an initial speed of 5ms^-1. when it hits the ground it rebounds vertically with half the speed it had when it hit the ground.

Q - find the height to which it rebounds
2. (Original post by ShOcKzZ)
can't do this dam question although im sure its not too difficult.

tennis ball his so that it moves vertically downwards from a height of 1m with an initial speed of 5ms^-1. when it hits the ground it rebounds vertically with half the speed it had when it hit the ground.

Q - find the height to which it rebounds
First, find the speed it hits the ground using the formula v^2=(u^2)+2as.

distance s=1 initial speed u=5 acceleration down a=g

so v^2=25+2g

Now consider its upwards flight.

u^2=(25+2g)/4 a=-g and v=0 at the max height.

Now using the same formula we can find s.

s=((v^2)-(u^2))/2a = (0-(25+2g))/-8g = (25+2g)/8g= 57cmto 2 sf.

(this is taking g as 9.8)
3. eh, excuse me for asking but wheres my damn rep?
4. (Original post by ShOcKzZ)
can't do this dam question although im sure its not too difficult.

tennis ball his so that it moves vertically downwards from a height of 1m with an initial speed of 5ms^-1. when it hits the ground it rebounds vertically with half the speed it had when it hit the ground.

Q - find the height to which it rebounds
On path to hit ground:

s = 1, u = 5, a = 9.8

v^2 = 5^2 + (2 * 9.8 * 1)
v^2 = 25 + 19.6
v = sq.root (44.6)
v = 6.68 ms^-1 (3 sf)

On way back up to reach max height:
(Remember its initial speed on way back up is then halved)

u = 3.34, a = -9.8, v = 0,

0 = (3.34)^2 + (2 * -9.8 * s)
0 = 11.1556 - 19.6s
19.6s = 11.1556
s = (11.1556)/19.6
s = 0.569 m (3.s.f.)

Therefore the ball rebounds to a height of 56.9 cm (3.s.f)
5. still no rep for you guys?
6. (Original post by TheWolf)
still no rep for you guys?
I don't want rep, I just wanted to do the question for my own benefit
7. (Original post by bono)
I don't want rep, I just wanted to do the question for my own benefit
lol and youve got enough reps anyways, like me
8. (Original post by TheWolf)
lol and youve got enough reps anyways, like me

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