Friction and Acceleration in Inclined Surfaces

[runningirl]

Homework Statement

A person pulls with a force of 40 N on two boxes at rest. The top box is 3.0 kg and the bottom box is 6.0 kg. The coefficient of kinetic friction between the floor and the larger box is .20 and the angle is 30 degrees.

a) if the smaller box doesn't slide on top of the larger box, what is the acceleration of the larger box?

b) Given your answer to part a, what must be the minimum value of the coefficient of static friction between the smaller box and the larger box?

Homework Equations

f=ma
f=(coefficient)*(normal force

The Attempt at a Solution

40=9(a)?

a=40/9?

i'm not even sure if this is the answer for part a.

 

[cegraves]

While your formula, f=ma, is mostly correct, you have not applied it properly.

The fact that the force is applied at an angle changes the situation, and you need to reconsider how you calculate the force.
Also, why I said mostly correct is because you failed to include the sum F=ma. You need to consider the coefficient of friction when solving for acceleration.
A piece of advice is to draw a force diagram. That will help you see all the forces.

Hope that helps you get moving in the right direction!