Question

If the crate shown here is moving at a constant speed in a straight line and the force applied is 310 N, what is the magnitude of the force of friction?
A.310 N
B.0 N
C.620 N

Answer 1

Answer:

$f_k = 310N$

the answer is A.

Explanation:

Using the laws of newton:

∑F = ma

where ∑F is the sumatory of forces acting in the system, m the mass and a the acelertion of the system.

Then, if the block is moving with constant velocity, its aceleration is equal to 0, so:

∑F = m(0)

∑F = 0

It means that:

F -$f_k$ = 0

where F is the force applied and $f_k$ is the friction force. Replacing the value of F, we get:

310N -$f_k$ = 0

Finally, solving for $f_k$:

$f_k = 310N$