# physics coursework

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17 years ago
#1
Hi
can anyone help me I am doing a bit of coursework that is called ENERGY CHANGES IN A BOUNCING BALL and one of the questions i was asked to answer was: Asumming there is no air-resistance how can you calculate the speed of the ball at the instant it hits the ground/

thanx
luv littleloz_87
0
17 years ago
#2
In terms of energy used the greater the height the greater the kinetic energy When the ball is heated, the heat energy given to the ball will affect the air molecules inside it, giving them more energy to collide and move faster and faster. This would result in more collisions of the air particles with the particles of the ball thus increasing the ball’s overall air pressure. With this increase of air pressure within the ball, the ball will deform less when it comes into contact with the floor than it would when it has a lower air pressure because constant, rapid collisions of the air molecules inside the ball help maintain the shape of the ball better at this higher pressure. Due to the ball deforming (or flattening) less, it loses less sound and heat energy and therefore has more energy to be used in motion resulting in the ball bouncing higher.
0
16 years ago
#3
I'm not sure if this will help but...

The velocity of the ball when it hits the ground can be calculated in two ways:

1. At the point where the ball hits the groud the gravitational potential enery (GPE) is zero as: U=mgh and h=0. Therefore the initial gravitational potential energy must have all been converted to kinetic enery (as there is no air resistance, therefore no GPE is converted to heat etc whilst falling). Hence kinetic energy= GPE ie: ½mv²=mgh
So if you know the mass of the ball and the hight from which the ball was dropped from, v can be calculated (using g=9.8)

2. One of the following kinematics equations can be used, depending on the information given:
s=½(v+u)t
v=u+at
v²=u²+2as
s=ut+½at²
where:
s=displacement
v=initial velocity (zero in your case)
u=final velocity (what you're trying to find)
a=acceleration (due to gravity for a bouncing ball. approx. 9.8)
t=time
Make sure you use negative signs appropriately (ie assign down as negative and up as positive) to make sure you end up with the right answer.

I hope this is helpful. If you have any questions, write to me at [email protected]

regards
A Dev
(yr 12, australia)
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