What is the coefficient of friction question?

[williamx11373]

Homework Statement

a boy uses a rope to pull a box weighing 300 Newtons across a surface with a constant velocity . The rope makes an angle of 30 degrees with the horizontal, and the tension in the rope is 100 Newtons. What is the coefficient of friction ??

The Attempt at a Solution

300 Newtons - 100 Newtons = 200netowns

200 Newtons x Cos30 = 173 ?




is this the correct way to go about it ?

 

[NeedPhysHelp8]

Well the easiest way to solve these kind of problems is to draw out a free body diagram. The thing to know about friction is that it only opposes the force parallel to the motion. Since the rope is at a 30 degree angle, the horizontal applied F= (100N)cos(30) = 86.6 N.
Now since the box is moving at constant speed the Force of friction must be equal to the applied force. So Ff = 86.6 N in opposite direction. Then you must know Ff = umg where mg is the weight. 86.6N = u(300N) and solve for the coefficient of friction