A 146N force is needed to pull a 350 N block across a horizontal surface at a constant speed by a rope making an angle of 50 degrees with the floor. Find the coefficient of friction.

F = force

f = friction

u = coefficient of friction

R = normal reaction force

a = Acceleration

m = mass of block

g = gravity

f = uR

F = Ma

Say the block is moving to the right.

The 146N force thus acts to the right, and the friction force to the left, since it resists movement.  

The 146N force acts to the right, but the horizontal component of it is 146 cos 50  = 93.84: So this is the force to the right.

Since F = uR and we're trying to find u, we need both F and R. R is easy to get since it is just m x g. This is in fact already given as the weight 350N. So R = 350.

The block is moving at a constant speed, so the force to the right must = the force to the left.

F = ma, so 93.84 - f = (350/g) x 0

This means f must be 93.84 also.  

so  we have f = uR,  

      93.84 = u x 350

so u = 0.268 or  

0.27 to 2dp.  

Hope you understand this.

Explanation: