Mechanical reasoning: Practice 1

10 original teaching questions with answers and explanations.

Instructions for this set

Use the idealised assumptions stated in each question. No friction or mechanical loss is included unless specified. These are conceptual exercises, not practical operating instructions.

Feedback mode has no time limit or negative marking. The optional timed challenge allows 15 minutes and uses the scoring shown on its rules screen. Those settings are not official assessment rules.

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  1. 1. An ideal horizontal lever is balanced about its pivot. A downward 60 N force acts 2 m to the left. What downward force is needed 3 m to the right? Ignore the lever weight.
    1. 20 N
    2. 30 N
    3. 40 N
    4. 90 N

    Reference: q-f2822f9-172 · Report this question

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    Answer: C. 40 N

    Both forces act perpendicular to the horizontal lever and produce opposing moments. Balance gives 60 times 2 = F times 3, so F = 40 N.
  2. 2. External gear A meshes directly with external gear B on parallel fixed axes. A turns clockwise when viewed from one side. Viewed from the same side, which way does B turn?
    1. Clockwise
    2. Anticlockwise
    3. It cannot turn
    4. Direction is independent of A

    Reference: q-64a8c9b-172 · Report this question

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    Answer: B. Anticlockwise

    Directly meshed external gears on parallel axes turn in opposite directions when viewed from the same side. B therefore turns anticlockwise.
  3. 3. External gear A has 20 teeth and turns at 90 rpm. It meshes directly, without slipping, with a 60-tooth external gear B. What is B speed?
    1. 15 rpm
    2. 30 rpm
    3. 90 rpm
    4. 270 rpm

    Reference: q-60076370-138 · Report this question

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    Answer: B. 30 rpm

    Directly meshed tooth counts and speeds satisfy 20 times 90 = 60 times B speed. Thus B turns at 90 times 20/60 = 30 rpm.
  4. 4. An ideal single fixed pulley lifts a 100 N load at constant speed. What pull is required, ignoring rope weight and friction?
    1. 25 N
    2. 50 N
    3. 100 N
    4. 200 N

    Reference: q-c88a389f-125 · Report this question

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    Answer: C. 100 N

    At constant speed the load has zero acceleration. A fixed pulley has ideal mechanical advantage one, so the rope tension and required pull equal the 100 N load.
  5. 5. A weightless ideal movable pulley holds a 120 N load at rest with two vertical rope sections sharing it equally. What is the tension in each section?
    1. 30 N
    2. 60 N
    3. 120 N
    4. 240 N

    Reference: q-69fe14a9-150 · Report this question

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    Answer: B. 60 N

    At rest the two equal upward tensions balance the 120 N load. The pulley adds no weight, so each tension is 120/2 = 60 N.
  6. 6. A 200 N force acts perpendicular to a surface and is distributed uniformly over 0.5 square metres. What is the pressure?
    1. 100 Pa
    2. 200 Pa
    3. 400 Pa
    4. 1,000 Pa

    Reference: q-b26feee9-121 · Report this question

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    Answer: C. 400 Pa

    Pressure equals normal force divided by area: 200/0.5 = 400 pascals.
  7. 7. Three external gears A, B and C on parallel fixed axes mesh in a line: A with B, B with C. Viewed from the same side, A turns clockwise. Which way does C turn?
    1. Clockwise
    2. Anticlockwise
    3. It is stationary
    4. It changes direction every turn

    Reference: q-75e5afde-160 · Report this question

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    Answer: A. Clockwise

    From the same viewing side, direction reverses at each external gear contact. Two reversals make C turn clockwise, the same direction as A.
  8. 8. A spring obeys F = kx with k = 100 N/m. What force stretches it by 0.04 m?
    1. 0.4 N
    2. 4 N
    3. 40 N
    4. 400 N

    Reference: q-e9212a4a-75 · Report this question

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    Answer: B. 4 N

    Substitute in the supplied law: 100 times 0.04 = 4 N.
  9. 9. In a lossless lift, a 50 N upward force raises a load vertically by 2 m at constant speed. What work does the lifting force do?
    1. 25 J
    2. 50 J
    3. 100 J
    4. 200 J

    Reference: q-33aa8a38-128 · Report this question

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    Answer: C. 100 J

    Work by a parallel force is force times distance: 50 times 2 = 100 joules.
  10. 10. An ideal lever doubles the applied force at the load. If the effort point moves 10 cm, how far does the load move under conservation of work?
    1. 2.5 cm
    2. 5 cm
    3. 10 cm
    4. 20 cm

    Reference: q-37526173-142 · Report this question

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    Answer: B. 5 cm

    Input work equals output work. Twice the output force requires half the movement, so the load moves 5 cm.

Review your method

Return to the mechanical reasoning lesson and identify the reasoning step behind each mistake before repeating the set.

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