mechanics question - will give rep. Watch

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ShOcKzZ
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#1
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#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
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Drederick Tatum
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(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)
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Drederick Tatum
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eh, excuse me for asking but wheres my damn rep?
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Nima
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(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)
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TheWolf
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still no rep for you guys?
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Nima
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(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
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TheWolf
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(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
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Nima
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(Original post by TheWolf)
lol and youve got enough reps anyways, like me
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