A block weighing 5.0 N is at rest on a horizontal surface. A 1.0 N upward force is applied to the block by an attached helium filled balloon with a massless string. What are the magnitude and direction of the force of the horizontal surface on the block?

Also, what would the free body diagram look like?

1 Answer
Sep 25, 2017

The surface provides an upward normal of 4.0 N. See Explanation for description of the free body diagram.

Explanation:

The block continues to be at rest on the horizontal surface. Therefore all forces must sum to zero, yielding #F_"net" = 0#.

There are 3 forces acting on the block:

  1. Its weight is a downward 5.0 N force
  2. The balloon lifts with a force of 1 N
  3. The surface provides an upward normal force, #F_N# that we have to calculate.

Let the upward direction be the positive direction.

#F_"net" = -5.0 N + 1 N + F_N = 0#
#F_N = 5.0 N - 1.0 N = 4.0 N#

The free body diagram would show upward forces of 1 N & 4 N and a downward force of 5 N.

I hope this helps,
Steve