A hammer with 10 J of kinetic energy hits a nail and pushes it 5.0 mm into a plank.

Question 16

A hammer with 10 J of kinetic energy hits a nail and pushes it 5.0 mm into a plank.

Both the hammer and nail come to rest after the collision.

What is the average force that acts on the nail while it moves the 5.0 mm?

A 0.050 N                    B 2.0 N                        C 50 N                         D 2000 N

Reference: Past Exam Paper – June 2011 Paper 12 Q19 & June 2016 Paper 11 Q19

Solution:

Answer: D.

The kinetic energy is converted into work done by the hammer in pushing the nail into the plank.

Since both the hammer and nail come to rest after the collision, all of the KE of the hammer has become ‘work done’. 

[Remember than both ‘work done’ and ‘kinetic energy’ has unit ‘joule’.]

Work done = Force × distance

10 = F × 5×10^-3

F = 10 / (5×10^-3) = 2000 N