Magnitude of Frictional Force

1. Sep 16, 2012

bcalkins

Hey,
I have a practice problem that I haven't been able to get and a test coming up. I've looked in the book for how to solve the problem but can't find anything. Would you mind helping, please?

Problem:
A 2 kg block is at rest on a dry, flat, horizontal table. A horizontal force with increasing magnitude is applied to the block (in the positive x direction). The block does not move until the applied force reaches a magnitude of 1.5N. What is the magnitude of the friction force by the table on the block when the applied force is 0.4 N?

Thank you!

2. Sep 16, 2012

jldibble

If an object is not accelerating, then the object is either experiencing zero forces or all of the forces are balanced (zero net force).

In this case, friction will push back on you with a force that is equal to your applied force until your applied force reaches 1.5N. So if you are pushing with a force of 0.4N, then the block (and in turn, the frictional force) will push back with a force of 0.4N

3. Sep 16, 2012

bcalkins

okay, thank you!