Frictional Force and acceleration

[karajo]

Homework Statement

The force applied to a cart is 10.5 N. The cart now moves toward the right at an acceleration also toward the right of 1.75m/s2. What are the magnitude and direction of the frictional force? The attempt at a solution
I found that my mass is 6kg. I have F, m, and a, but I am unsure how to find the frictional force.

 

[Doc Al]

What forces act on the cart? Draw yourself a free body diagram, then apply Newton's 2nd law.

 

[Doc Al]

I found that my mass is 6kg.

How did you determine the mass? I assume is was given elsewhere in the problem?

 

[karajo]

How did you determine the mass? I assume is was given elsewhere in the problem?

I found mass by using F=ma
Force=10.5N
acceleration=1.75m/s2

I drew a free body diagram with Force in the positive direction, friction pulling the negative way, and acceleration in the positive direction. Also the Normal force going up and mass*gravity going down.

 

[Doc Al]

I found mass by using F=ma
Force=10.5N
acceleration=1.75m/s2

That won't work. For one thing, Newton's 2nd law should be written as $\Sigma F = ma$, where $\Sigma F$ stands for the net force. In this problem, all you know are the applied force and resulting acceleration.

You need to be given the mass; there's not enough information to figure it out. Make sure you've posted the full problem, exactly as it was given.

I drew a free body diagram with Force in the positive direction, friction pulling the negative way, and acceleration in the positive direction. Also the Normal force going up and mass*gravity going down.

Good.

 

[karajo]

Oh, I have a mass of 3.23 kg for the cart.

 

[Doc Al]

Oh, I have a mass of 3.23 kg for the cart.

That makes more sense. Now you can figure out the net force.