Kinetic energy

[Niha afzal]

I used the kinematic equations

To first find mass from the k.e given

And in the secound part I used the mass to calculate the new k.e .... I attached my working

[studiot]

Calculations refer to the position of the centre (of gravity) of the ball.

They give you the ball diameter because this is not negligable.

 

For instance the ball falls from where the top is at +80 cm to where the bottom is at 0 cm. (reckoning up as positive).

So how far does the ball fall, ie what is its loss of PE?

Edited March 28, 2016 by studiot

[Niha afzal]

Oh so il take the height as .8-0.04 meters ....

Then the p.e will be mass× -9.81 × .8-0.04 ?

[studiot]

 

Oh so il take the height as .8-0.04 meters ....

Then the p.e will be mass× -9.81 × .8-0.04 ?

 

 

Er Hem

 

How big is the ball?

[Niha afzal]

Diameter 8 cm .. 0.08 m

[studiot]

 

So how far does the ball fall, ie what is its loss of PE?

 

Let me rephrase this

 

So how far does the centre of the ball fall, ie what is its loss of PE?

 

 

Edited March 28, 2016 by studiot

[Niha afzal]

Okay okay ojaay maybe we take the height as 80 -8 cm.... bcz we start the height frm center of gravity of baallll and end it at COG which makes a complete diameter

[studiot]

OK so why do we need to calculate all these kinetic quantities?

 

Walk me through the sequence of energies (KE and PE) at the important stages in the path of the ball.

 

See if you can puzzle it out first, before I tell you.

Edited March 28, 2016 by studiot

[Niha afzal]

Hmn so the potential energy at thestart of motion convert to kinetic energy (ke ) the ke is max at the bottom when ball is about to hit the groud so the potential energy at the begning converted to k.e

 

Now since the balll after rebound didnt go back to 80 cm some energy must have been lost as heat light ..

But in the upwards motion to the k.e getconverted potential energy.

Thats all I know about k.e and g.e

Edited March 28, 2016 by Niha afzal

[studiot]

What you know is correct.

 

you know the height of the drop and the height of the bounce back, and the PEs must be in the same ratio as these heights.

 

you know that all the drop PE is converted to KE and similarly all the bounce back PE starts off as KE, again in the same ratio

 

Can you put this into figures now?

[Niha afzal]

Yessssss! !! :D