IB Physics SL A.3.4 Work by Constant Force Question Bank

Practise calculating work from force, displacement and kinetic-energy change, including zero work and frictional losses.

Exam points

Apply W = Fs cosθ to decide when work is zero, negative or positive for forces and displacement.
Calculate work from force, distance, rotations and kinetic-energy change in braking and impact situations.
Link work done by friction, air resistance or a brake to the energy transferred from moving objects.

[Maximum number: 2]

This question is in two parts. Part 1 is about two children on a merry-go-round. Part 2 is about electric circuits.

Part 1 Two children on a merry-go-round
Aibhe and Euan are sitting on opposite sides of a merry-go-round, which is rotating at constant speed around a fixed centre. The diagram below shows the view from above.

Figure for Question A.3.4—Work by constant force question 1 — IB Physics SL

Aibhe is moving at speed $1.0 \mathrm{~ms}^{-1}$ relative to the ground.

Euan drags his foot along the ground to act as a brake. The merry-go-round comes to a stop after 4.0 rotations. The radius of the merry-go-round is 1.5 m . The average frictional force between his foot and the ground is 45 N . Calculate the work done.

distance travelled by Euan $=4.0 \times 2 \pi \times 1.5(=37.70 \mathrm{~m})$ ;

W\left(=F_{a v} d=45 \times 37.70\right)=1700(\mathrm{~J}) ;

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A.3.4—Work by constant force question 1