Question

A 14 kg mass is resting on a horizontal surface. A 240 N force is applied to pull the mass along the surface. The coefficient of kinetic friction, k, between the mass and the surface is 0.5 and the coefficient of static friction, s, is 0.7

Find the net force on the mass.

Answer 1

you know the relation between the frictional force and thr coefficient of friction.

Answer 2

@ thr - the

Answer 3

The maximum force, fstatic,max that can be placed on the mass and have it not move is 96.04 N.

Answer 4

Not clear whether initial net force, static, or later net force, sliding, is sought.

Answer 5

I think that it is looking for the initial net force.

Answer 6

I think the net force is zero based on the answers to the following questions I found online:

1. A block of mass m is pulled at constant velocity across a horizontal surface by a string as in Figure 5-39. The
magnitude of the frictional force is (a) mkmg. (b) T cos q. (c) mk(T - mg). (d) mkT sin q. (e) mk(mg + T sin q).

THIS IS THE RIGHT ANSWER --> (b) The net force is zero.

2. A block of wood is pulled by a horizontal string across a horizontal surface at constant velocity with a force
of 20 N. The coefficient of kinetic friction between the surfaces is 0.3. The force of friction is (a) impossible to
determine without knowing the mass of the block. (b) impossible to determine without knowing the speed of the
block. (c) 0.3 N. (d) 6 N. (e) 20 N.

THIS IS THE RIGHT ANSWER --> (e) The net force is zero.

Answer 7

Also, if Mk (coefficeint fo kinetic friction) is > than Ms, then the block will slide by itself

however in this case, Ms>Mk so the force is needed to move the mass.

Answer 8

I now agree, the NET force is zero because there is no acceleration and the forces cancel each other. thanks. In the second example, they ask for the force of friction, which is not zero but equal t the force pulling against it.