Which statement includes a correct unit? A energy = 7.8 N s

Question 7

Which statement includes a correct unit?

A energy = 7.8 N s

B force = 3.8 N s

C momentum = 6.2 N s

D torque = 4.7 N s

Reference: Past Exam Paper – June 2015 Paper 13 Q1

Solution:

Answer: C.

The unit Ns indicates the product of the quantity having unit N and quantity having unit s. That is, force × time.

Energy is force × distance. [A is incorrect]

The unit of force is N, so N s is an incorrect unit for force. [B is incorrect]

Force = Δp / t

Δp = F × t

So, momentum can have unit N × s. [C is correct]

Torque = Force × distance

So, unit of torque: N m, not N s. [D is incorrect]