Question

Man A takes 5 seconds to stop a 1 kg ball thrown at 10 m/s at him. Man B takes the same time to return the same ball coming at him at 5 m/s exactly in the opposite direction with same speed. Who applied more force?

• A. Man A
• B. Man B
• C. Both of them applied same amount of force
• D. Wrong question, No force was applied to stop the ball.

Answer 1

The correct option is C

Both of them applied same amount of force

$F=\frac{\Delta p}{\Delta t}$

For Man A

Ball is coming at 10 m/s

Lets say $\to$ u = + 10 m/s

v = 0 ($\because$ as ball stops)

m = 1 kg

$\Delta t$ = 5 sec

$\Rightarrow F=\frac{\Delta p}{\Delta t}=\frac{\Delta mv}{\Delta t}=\frac{m\Delta v}{\Delta t}$

$=1\times \frac{(v-u)}{5}=1\times \frac{(0-10)}{5}$

|F| = 2 N

For Man B

u = + 5 m/s v = - 5 m/s

$\Delta t$ = 5 sec m = 1 kg

$F=1\times \frac{(-5-5)}{5}=-2N$

|F| = 2 N

So both Man A & Man B applied the same force