Question

Block B, which has a mass of 45 kg, is moving at a constant velocity across a flat surface. As shown in the diagram, it is being pulled forward by a force of 100 N. What is the magnitude of the force represented by the left-pointing arrow in the diagram?

0 N
440 N
44 N
100 N

Answer 1

`100\; {\rm N}`.

Step-by-step explanation:

The block is in a translational equilibrium since the velocity of the block is constant.

Because velocity of the block is not changing, acceleration of the block would be
`0`. By Newton's Laws of Motion, the net force on this block would also be
`0\!`, meaning that forces on the block would be balanced.

Specifically, forces on this block need to be balanced in the horizontal direction. There are two forces on this block in that direction:

• The
  `100\; {\rm N}` force pointing to the right, and
• The force pointing to the left, which needs to be found.

For these two forces to balance each other, their magnitudes need to be the same. Hence, the force pointing to the left should also have a magnitude of
`100\; {\rm N}`.