Question

you can complete this review up to 3 times. it will be worth 2.5 points extra credit onto the exam.
question 14
1 pts
a student sets a small box with a mass of \m\ on a platform scale. the object is tied to a piece of string which gently pulls upwards on the object with a force of $f_t$. the object remains motionless at rest on the scale and the scale still has a reading on it which is greater than zero.
which of the following equilibrium equations correctly describes the forces acting on the object?
$f_n = mg + f_t$
$f_n = mg$
$f_t + f_n = mg$
$f_a + f_n = mg + f_t$

Explanation:

Step1: Analyze Forces on Object

The object has three forces: gravitational force \( mg \) (downward), normal force \( F_N \) (upward from scale), and tension \( F_T \) (upward from string). Since it's in equilibrium (rest), upward forces sum to downward forces.

Step2: Set Up Equilibrium Equation

Upward forces: \( F_N + F_T \). Downward force: \( mg \). So equilibrium equation is \( F_T + F_N = mg \).

Answer:

\( F_T + F_N = mg \) (the third option, e.g., if options are labeled as 1. \( F_N = mg + F_T \), 2. \( F_N = mg \), 3. \( F_T + F_N = mg \), 4. \( F_A + F_N = mg + F_T \), then the answer is the third option with this equation)