What is the magnitude of the frictional force acting on the crate?

[moondawg]

Homework Statement

A crate with a total mass of 50 kg is initially at rest on a level floor. A horizontal force of 150N pushes the crate across the floor at a constant acceleration of 1.2m/s². What is the magnitude of the frictional force acting on the crate?

Homework Equations

The Attempt at a Solution

So this question seems so basic but I know I'm doing it wrong. All i did was plugged the numbers into the F=$$\mu$$N formulas and got $$\mu$$= .31. But in using that formula I am not even taking into account the acceleration and I don't know what to use in order to take it into account?! Someone please explain

 

[Stonebridge]

It's just F=ma on the crate, but remembering that there are 2 forces acting here; the 150N and the friction.

 

[ThyQuotidian]

 

[a.ratnaparkhi]

It means that if 50N force is foreword,then frictional force must act backward.
let net force be fn.
so according to the free body diagram,
fn=150-f (say frictional force be f) ...1

fn=ma=50*1.2
Now from this you'll get fn & from equation 1, you'll get f.