Vertical spring physics

1. May 10, 2008

fiziksfun

An 5 kg block is fastened to the top of a vertical spring (perpendicular to the floor) with a spring constant of 1000 N/m. A 3 kg block sits on top of the 5 kg block.

The springs are pushed down so that they oscillate.

I need help finding the magnitude of the maximum acceleration the blocks can obtain while still remaining in contact. I have no idea where to begin.

2. May 10, 2008

Hootenanny

Staff Emeritus
HINT: Consider the forces acting on the 3kg block, which force will be zero when the blocks lose contact?

3. May 10, 2008

fiziksfun

Ok so when the blocks lose contact, the force of the spring-mass will be equal to the force of gravity on the 3 kg block.

M(3)*a=-2mg, is this correct?

4. May 10, 2008

Hootenanny

Staff Emeritus
You've still not answered my first question. What are the forces acting on the top block?

Last edited: May 10, 2008
5. May 10, 2008

fiziksfun

The forces acting on the block are gravity and the force of the spring, correct? Or friction??

6. May 10, 2008

Hootenanny

Staff Emeritus
Correct, but what I was trying to get at is that the force of the spring acts through the normal force exerted on the block. Hence, the net force acting on the block is $N - mg$. Can you now use this information to write an equation using Newton's second law?

7. May 11, 2008

fiziksfun

ma = N - mg

but what is the magnitude of the normal force !?!?!? kx !?

8. May 13, 2008

Hootenanny

Staff Emeritus
Correct! And what do you know about the normal force when the block leaves the surface of the 5kg block?