Buoyancy and mechanical energy

1. May 2, 2007

future_vet

1. The problem statement, all variables and given/known data
A block of unknown material weighs 50 N in air and 20 N in water. What is the buoyant force of water?

2. Relevant equations
I know how to calculate density etc. I thought the formula to use was -density x V x g but it's not correct.

1. The problem statement, all variables and given/known data
A x Kg mass is attached to a horizontal spring of constant 20 N/m and set into harmonic motion with an amplitude = 0.2m. What is the total mechanical ernergy of the system?

I have no idea what to do... Some help would be greatly appreciated. Thanks!

2. May 2, 2007

3. May 2, 2007

future_vet

I was thinking it would be 50 - 20 = 30 but it seems a bit too simple to be true...

4. May 2, 2007

future_vet

So for the second:
0.5 * 25 * 0.2^2 = 0.50J ?

THANK YOU!

5. May 2, 2007

Mentz114

It's simple and it's true.

I can't check your second answer because I can't see what the mass is.

 E = 1/2ka^2 - whoops, you don't need the mass, so you're right there also.

Last edited: May 2, 2007