Question

A student pulls horizontally on a block with a spring scale. The block reads 24.5 Newtons before the block starts to move. It reads 23.7 Newtons as she pulls the block at a constant velocity. How should she explain this?

Answer 1

Answer:

The coefficient of friction causes the force on the object to be less than its initial reading on the spring scale.

Explanation:

Since the block reads 24.5 N before the block starts to move, this is its weight. Now, when the block starts to move at a constant velocity, it experiences a frictional force which is equal to the force with which the student pulls.

Now, since the velocity is constant so, there is no acceleration and thus, the net force is zero.

Let F = force applied and f = frictional force = μN = μW where μ = coefficient of friction and N = normal force. The normal force also equals the weight of the object W.

Now, since F - f = ma and a = 0 where a = acceleration and m = mass of block,

F - f = m(0) = 0

F - f = 0

F = f

Since the force applied equals the frictional force, we have that

F =  μW and F = 23.7 N and W = 24.5 N

So, 23.7 N = μ(24.5 N)

μ = 23.7 N/24.5 N

μ = 0.97

Since μ = 0.97 < 1, the coefficient of friction causes the force on the object to be less than its initial reading on the spring scale.