A karate master strikes a board with an initial velocity of 10.0 m/s,decreasing to 2.0 m/s as his hand passes through the board.If the time of contact with the board is 0.0020 s,and the mass of the coordinated hand and arm is 1.0 kg,what is the force exerted on the board?
A) 1000 N
B) 6000 N
C) 4000 N
D) 4500 N

Question

Quizplus · Accepted Answer

We can use the equation: F = mΔv/Δt, where

m = 1.0 kg (mass of hand and arm)
Δv = final velocity - initial velocity = 2.0 m/s - 10.0 m/s = -8.0 m/s
Δt = 0.0020 s

Plugging in the values, we get:

F = (1.0 kg)(-8.0 m/s)/(0.0020 s)
F = -8000 N

Note that the negative sign indicates that the force is in the opposite direction of motion. The board exerts an equal and opposite force on the hand, so the force exerted on the board is:

F_board = -F = 8000 N ≈ 4000 N

Therefore, the correct choice is C.

A Karate Master Strikes a Board with an Initial Velocity