Question

What is the gravitational energy (relative to the unstretched surface of the trampoline) of the 20 kg ball at its apex 2 m above the trampoline? G= 10 N/kg

Answer 1

That is a very unusual unit for G ( I assume you mean g the acceleration due to gravity)

It is normally expressed as m/s^2 (although the unit you have is dimensionally the same)

Gravitational energy - also known as Potential Energy PE is given by

PE= mgh

You know all the terms - so just multiply them to get PE

Answer 2

ok thanks! now how about when at maximum stretch at the bottom of the motion, what is the sum of the elastic and gravitational energy of the ball? i know the v= 0. I'm so confused! sorry haha

Answer 3

Do you know the elastic constant for the trampoline (spring constant or k?)

Answer 4

ono they didn't give me one.. this is the whole qu

Use g=10 N/kg in this assignment.

1. What is the gravitational energy (relative to the unstretched surface of the trampoline) of the 20 kg ball at its apex 2 m above the trampoline?
2. What is the kinetic energy of the ball just before impacting the trampoline?
3. At maximum stretch at the bottom of the motion, what is the sum of the elastic and gravitational energy of the ball?
4. What conclusions can you draw from the answers found above?

Answer 5

When the ball hits the trampoline it has 'lost' the PE that you calculated above.

It starts to stretch the trampoline spring - and CONTINUES to lose PE as it fall below the level of the flat trampoline.

At maximum stretch (x) the ball has fallen h=x

So its loss of PE is mg(h+x)

This energy is stored in the spring (trampoline) and is given by 0.5kx^2

There is no kinetic energy at the max stretch as all is static so

mg(h+x) = 0.5kx^2

If you know k then you can solve for x

Answer 6

so basically, i cannot really solve for number 3. its just an explanation.

Answer 7

Yes - yo ucannot calculate the actual value for x without k

also the question is slightly misleading - it is the SPRING (not the ball) that has the Elastic energy.

Just bear in mind that at all point in the system no Energy is added or lost - so the sum of PE, KE and Elastic Energy is constant at all times.

Also remember that PE is RELATIVE to a given datum level.

Answer 8

ok thank you!!

Answer 9

I'm sorry - I misread your point

You cannot calculate x - but you can say that the sum of the elastic and gravitational energy is equal to the change in gravitational energy from the original position ( 2m above the surface to the lowest position (somewhere BELOW the surface of the trampoline)

Answer 10

okay! haha thanks :)