Question

A block is moving at constant speed due to a horizontal force pulling to the right. The coefficient of kinetic friction, Hk, between the block and the surface is 0.20 and the mag- nitude of the frictional force is 100.0 N, what is the weight of the block? (a 400 N (b) 600 N (c) 500 N (d) 267 N

Answer 1

Answer:

c) 500 N

Explanation:

If the block moves with constant speed there is no acceleration. We draw a free body diagram and define the forces on the body.

$F_{f}=FrictionForce\\F_{e}=ExternalForce\\N=NormalForce\\W=Weight$

The equation for the frictional force is:

$F_{f}=N*H_{k}$

Where $H_{k}$ is the kinetic friction coefficient. We write the equilibrium equation in the y direcction:

$\sum F_{y}\rightarrow N-W=0\\N=W$

We replace this result in the equation for the frictional force:

$F_{f}=W*H_{k}$

We replace the data given by the exercise and find the weight

$W=\frac{F_{f}}{H_{k}}\\W=\frac{100}{0.2}=500\: N$