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

c) 500 N

Step-by-step 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=(F_(f))/(H_(k))\\W=(100)/(0.2)=500\: N`