Question

a crane has a large brick attached to its hook. two forces are acting on the brick, as shown below.

which of the following statements is true?
a. the forces acting on the brick are balanced.
b. an unbalanced force is acting on the brick.
c. the brick is at rest.
d. a net force of 5 newtons is pulling the brick upward.

Explanation:

Identify the given forces acting on the brick

The image shows two vertical forces acting on the brick:

• An upward force (tension from the crane hook): \(F_{\text{up}} = 7,205\text{ N}\)
• A downward force (gravity/weight of the brick): \(F_{\text{down}} = 7,210\text{ N}\)

Calculate the net force on the brick

To find the net force (\(F_{\text{net}}\)), we subtract the upward force from the downward force:

$$ F_{\text{net}} = F_{\text{down}} - F_{\text{up}} = 7,210\text{ N} - 7,205\text{ N} = 5\text{ N (downward)} $$

Since the net force is not zero, the forces acting on the brick are unbalanced.

Evaluate the given statements

• A. The forces acting on the brick are balanced.

This is false because the upward and downward forces are not equal in magnitude (\(7,205\text{ N}
eq 7,210\text{ N}\)).

• B. An unbalanced force is acting on the brick.

This is true because there is a non-zero net force of \(5\text{ N}\) acting on the brick.

• C. The brick is at rest.

This cannot be determined to be true; since there is a net unbalanced force, the brick must be accelerating downward.

• D. A net force of 5 newtons is pulling the brick upward.

This is false because the downward force (\(7,210\text{ N}\)) is greater than the upward force (\(7,205\text{ N}\)), meaning the net force of \(5\text{ N}\) is pulling the brick downward, not upward.

Answer:

• (A) The forces acting on the brick are balanced.
• (B) An unbalanced force is acting on the brick. (Correct answer)
• (C) The brick is at rest.
• (D) A net force of 5 newtons is pulling the brick upward.