Everything Science Grade 11

12.6 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

Example 36: Merry-go-round

QUESTION

Several children are playing in the park. One child pushes the merry-go-round with a force of

50 N. The diameter of the merry-go-round is 3,0 m. What torque doesthe child apply if the

force is applied perpendicularly at point A?

A

diameter = 3 m

F

SOLUTION

Step 1 : Identify what has beengiven

The following has beengiven:

• the force applied, F = 50 N


• the diameter of the merry-go-round, 2 r = 3 m, therefore r = 1,5 m.
  The quantities are in SIunits.

Step 2 : Decide how to approach the problem

We are required to determine the torque appliedto the merry-go-round. We can

do this by using:

τ = F⊥· r

We are given F⊥and we are given the diameter of the merry-go-round. Therefore,

r = 1,5 m.

Step 3 : Solve the problem

τ = F⊥· r

= (50N)(1,5m)

= 75N· m

Step 4 : Write the final answer

75 N· m of torque is applied to the merry-go-round.

Tip

Torques: the direction
of a torque is either
clockwise or anticlock-
wise. When torques are
added, choose one di-
rection as positive and
the opposite direction as
negative. If equal clock-
wise and anticlockwise
torques are applied to an
object, they will cancel
out and there will be no
net turning effect.