Question 22N.2.SL.TZ0.4
| Date | November 2022 | Marks available | [Maximum mark: 5] | Reference code | 22N.2.SL.TZ0.4 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Draw, Explain | Question number | 4 | Adapted from | N/A |
A mass is attached to one end of a rod and made to rotate with constant speed in a vertical circle.
The scale diagram shows the weight W of the mass at an instant when the rod is horizontal.
Draw, on the scale diagram, an arrow to represent the force exerted on the mass by the rod.
[2]
horizontal component of any length to the left ✓
vertical component two squares long upwards ✓
E.g.
Ignore point of application.
Award [1] max if arrowhead not present.
Most just added the horizontal component. Not many centrifugal forces, but still a few. Very few were able to score both marks, so this question proved to be challenging for the candidates.
Explain why the magnitude of the force exerted on the mass by the rod is not constant.
[3]
ALTERNATIVE 1
the net/centripetal force has constant magnitude ✓
the direction of the net/centripetal force constantly changes ✓
this is achieved by vector-adding weight and the force from the rod
OR
the force from the rod is vector difference of the centripetal force and weight ✓
ALTERNATIVE 2
at the top Frod = Fc − W ✓
at the bottom, Frod = Fc + W ✓
net F/Fc is constant so the force from the rod is different «hence is changing» ✓
Accept reference to centripetal or net force indistinctly.
Allow reference to centripetal acceleration.
Many got into a bit of a mess with this one and it was quite difficult to interpret some of the answers. If they started out with the net/centripetal force being constant, then it was often easy to follow the reasoning. Starting with force on the rod varying often led to confusion. Quite a few did not pick up on the constant speed vertical circle so there were complicated energy/speed arguments to pick through.
