These seven original conceptual questions mix the Mechanical Engineering skills. Write your own answer first, then compare your method and units with the explanation.
This page is part of the SPM subjects and learning resources section.
Questions
Q1. A force of 30 N acts perpendicular to a spanner at 40 cm from the bolt. Find the moment in N m.
Answer
40 cm = 0.40 m. Moment = 30 N × 0.40 m = 12 N m.
Q2. A 500 N load sits 0.8 m from a pivot. What force at 2.0 m on the other side balances it?
Answer
Load moment: 500 × 0.8 = 400 N m. F × 2.0 = 400, so F = 400 ÷ 2.0 = 200 N.
Q3. A force of 80 N acts on an area of 0.04 m². Find the pressure in Pa.
Answer
Pressure = 80 N ÷ 0.04 m² = 2 000 Pa.
Q4. Gear P has 15 teeth and drives gear Q with 45 teeth. P turns at 90 revolutions per minute. Find Q’s speed.
Answer
Speed of Q = 90 × 15 ÷ 45 = 1 350 ÷ 45 = 30 revolutions per minute. Q has three times the teeth, so it turns at one third of the speed. This assumes the teeth mesh without slipping.
Q5. A student multiplies 50 N by 25 cm and writes 1 250 N m. What is wrong, and what is the correct moment?
Answer
The distance was not converted. 25 cm = 0.25 m, so the moment is 50 × 0.25 = 12.5 N m. The error is a factor of 100.
Q6. Explain, using a labelled diagram in words, why pushing a door near its hinge is harder than pushing it near the handle.
Answer
Label the hinge as pivot P, the push as force F and the distance from P as d.
The moment is F × d. Near the hinge, d is small, so the same F gives a small moment and the door resists moving. Near the handle, d is larger, so the same push gives a larger moment and the door turns more easily. This assumes the push is perpendicular to the door.
Q7. A student writes: “A longer ramp needs less force to push a box up.” Give two assumptions and rewrite the claim.
Answer
Assumptions: the box is pushed at a steady speed, and friction is small or similar on both ramps.
Rewrite: “For the same height, a longer ramp needs a smaller pushing force if friction is small and the box moves at a steady speed, because the work is spread over a longer distance.”
If you got these wrong
- Q1 to Q3, Q5: read check units in a conceptual calculation.
- Q6: read explain a principle with a labelled diagram, then link an observation to a mechanical model.
- Q4, Q7: read review an explanation for missing assumptions.
Build a timed set with the timed practice session builder and check your writing with the structured answer self-review. For a teacher to review your working, see online one-to-one Mechanical Engineering tuition.