Question

Mary pushes a crate by applying force of 18 newtons. Unable to push it alone, she gets help from her friend, Anne. Together they apply a force of 43 newtons, and the crate just starts moving. If the coefficient of static friction is 0.11, what is the value of the normal force?

Answer 1

answer is 3.9 x 10^2

Answer 2

This problem is relatively simple, in order to solve this problem the only formula you need to know is the formula for friction, which is:

Ff = UsN

where Us is the coefficient of static friction and N is the normal force.

In order to get the crate moving you must first apply enough force to overcome the static friction:

Fapplied = Ff

Since Fapplied = 43 Newtons:

Fapplied = Ff = 43 = UsN

and it was given that Us = 0.11, so all you have to do is isolate N by dividing both sides by 0.11

43/0.11 = N = 390.9 which is approximately 391 or C. 3.9x10^2