Question

URGENT

Answer 1

A light spring with force constant 3.35 N/m is compressed by 7.80 cm as it is held between a 0.350-kg block on the left and a 0.700-kg block on the right, both resting on a horizontal surface. The spring exerts a force on each block, tending to push the blocks apart. The blocks are simultaneously released from rest. Find the acceleration with which each block starts to move, given that the coefficient of kinetic friction between each block and the surface is 0, 0.050, and 0.412. (Let the coordinate system be positive to the right and negative to the left. Indicate the direction with the sign of your answer. Assume that the coefficient of static friction is the same as the coefficient of kinetic friction.)
(a) μ = 0
heavier block m/s2
lighter block m/s2

(b) μ = 0.050
heavier block m/s2
lighter block m/s2

(c) μ = 0.412
heavier block m/s2
lighter block m/s2

Answer 2

I know it. Do you know how to even start it...?

Answer 3

Well, I was just going to use the 1/2 kx^2 but not for sure.

Answer 4

Do you have a guess yet?

Answer 5

I do not.

Answer 6

Because it is dealing with 2 at a time...

Answer 7

i thnk its C but i may be wrong, its been a while since ive done it

Answer 8

No no It wants a value for each of those!

Answer 9

oh then i have no idea, i wasnt taught like that..

Answer 10

The force of a spring is defined by Hook's Law: F = -kx, where k is the force constant and x is the displacement from the origin of the spring.

To solve your first problem, friction is not considered, as u = 0.
You know that the spring will exert the same force on each mass (it is the same spring, this is logical). However, Newton's 2nd Law tells us F=ma. So even though the force is the same, the acceleration is not because it depends on the mass of the object.

So you simply need to use a force of magnitude kx and then divide this value by the mass of the block to get their accelerations.

======================
When friction is a factor, friction will resist movement. So you will need to know that:

Ff = u Fn ; where Fn is the normal force. Since the blocks are not sinking into the surface, the Fn must be equal to the weight of the blocks. Weight is simply equal to mass times gravitational acceleration (W = mg).

You will need to find the force like in the first part, but then subtract the Ff since this will inhibit motion. Then divide by the mass of the block like before and find acceleration.

Answer 11

So for the first I say 3.35/.35?

Answer 12

@Pompeii00

Answer 13

F=ma so A=F/m

The F=kx
??

Answer 14

You last statement is right:

F = ma, a = F/m ; F = kx
For the 0.350 kg block: a = kx / m = (3.35)(0.078) / (0.350). It is being pushed left, so you should also include a negative sign with it, I believe your problem states.

Answer 15

Got ya. Thanks so much. You just saved me like 4 points.

Answer 16

No problem! Just remember for the friction cases F = kx - Ff