Question

select the correct answer. tori experiments with pulleys in physics class. she applies 70 newtons of force to a single pulley to lift a bowling ball. by adding another pulley, shed get a mechanical advantage of 2. whats the minimum input force shell need to lift the ball if she adds another pulley?
a. 2 n
b. 35 n
c. 68 n
d. 70 n
e. 140 n

Explanation:

Step1: Recall mechanical - advantage formula

The formula for mechanical advantage (MA) is $MA=\frac{Output\ Force}{Input\ Force}$. When she used one pulley, $MA = 2$ and $Input\ Force=70\ N$. First, find the output force (weight of the bowling - ball). So, $Output\ Force=MA\times Input\ Force = 2\times70 = 140\ N$.

Step2: Calculate new input force with new MA

When she adds another pulley, the mechanical advantage doubles (assuming ideal conditions). So the new $MA = 4$. Using the formula $MA=\frac{Output\ Force}{Input\ Force}$, and since $Output\ Force = 140\ N$ and $MA = 4$, then $Input\ Force=\frac{Output\ Force}{MA}=\frac{140}{4}=35\ N$.

Answer:

B. 35 N