Simple Machines

Practise Simple Machines for FBISE Grade 9–10 Physics (Grade 9–10): 8 multiple-choice questions with instant checking and worked explanations. Free, no sign-up.

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1. Question 1

   An inclined plane of length $6\mathrm{m}$ is used to raise a $300\mathrm{N}$ box to a platform $2\mathrm{m}$ high. If the friction force opposing the motion along the plane is $20\mathrm{N}$, what effort force parallel to the incline is required to push the box at a constant speed?
   • A$80\mathrm{N}$
   • B$120\mathrm{N}$
   • C$100\mathrm{N}$
   • D$140\mathrm{N}$
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   Answer: B) $120\mathrm{N}$

   The weight component acting down the plane is $300\mathrm{N}\times \sin \theta$, and $sin\theta =\frac{2}{6}$ for a 2 m rise over a 6 m length, giving $100\mathrm{N}$. Because the box moves at constant speed, the effort must balance this component plus the $20\mathrm{N}$ friction, so $100+20=120\mathrm{N}$. The $100\mathrm{N}$ option ignores friction, $80\mathrm{N}$ subtracts it, and $140\mathrm{N}$ adds it twice.

2. Question 2

   A weight of $200\mathrm{N}$ is raised $1\mathrm{m}$ along an inclined plane of length $4\mathrm{m}$ having an efficiency of $50\%$. The same weight is then raised an additional $1\mathrm{m}$ vertically using a pulley system operating at $80\%$ efficiency. What is the total work input required to complete both operations?
   • A$500\mathrm{J}$
   • B$650\mathrm{J}$
   • C$800\mathrm{J}$
   • D$1000\mathrm{J}$
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   Answer: B) $650\mathrm{J}$

   The work needed to raise the weight is the weight times the vertical displacement. For the inclined plane the output work is $200\mathrm{J}$, and because the machine is only 50 % efficient the input work is $200/0.50=400\mathrm{J}$. For the pulley the output work is also $200\mathrm{J}$, and with 80 % efficiency the input work is $200/0.80=250\mathrm{J}$. Adding the two inputs gives $650\mathrm{J}$. The other options arise from mixing up efficiency with mechanical advantage, using the incline length as a height, or treating machines as energy multipliers.

3. Question 3

   A heavy crate is lifted using a lever system where an effort of $50\mathrm{N}$ is applied at a distance of $2\mathrm{m}$ from the fulcrum. The lever moves the load of $150\mathrm{N}$ located $0.5\mathrm{m}$ on the other side of the fulcrum through a height of $0.2\mathrm{m}$, while the effort moves through a distance of $0.8\mathrm{m}$. What is the thermal energy dissipated due to friction during this operation?
   • A$10\mathrm{J}$
   • B$40\mathrm{J}$
   • C$30\mathrm{J}$
   • D$70\mathrm{J}$
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   Answer: A) $10\mathrm{J}$

   The effort force does $50\mathrm{N}\times 0.8\mathrm{m}=40\mathrm{J}$ of work on the lever. The load is raised $0.2\mathrm{m}$, so the useful work delivered is $150\mathrm{N}\times 0.2\mathrm{m}=30\mathrm{J}$. The difference, $10\mathrm{J}$, is dissipated as thermal energy due to friction. The other options represent either the useful work alone, the total input work, or an incorrect addition of the two quantities.

4. Question 4

   A wheel and axle system has a wheel radius of $50\mathrm{cm}$ and an axle radius of $10\mathrm{cm}$. If an effort of $40\mathrm{N}$ is required to lift a load of $160\mathrm{N}$, what is the efficiency of this system?
   • A$75\%$
   • B$20\%$
   • C$80\%$
   • D$125\%$
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   Answer: C) $80\%$

   Efficiency of a simple machine is the ratio of its mechanical advantage to its velocity ratio. Here MA = $160/40=4$ and VR = $50/10=5$, so efficiency = $4/5=0.80$ or 80 %. The other options arise from swapping the ratios, ignoring forces, or dividing the radii in the wrong order.

5. Question 5

   Why does using a longer ramp to load a heavy cabinet onto a truck make the task feel easier?
   • AIt reduces the gravitational force acting on the cabinet.
   • BIt increases the mechanical efficiency of the system to $100\%$.
   • CIt reduces the required input force by increasing the distance.
   • DIt decreases the total work needed to reach the top.
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   Answer: C) It reduces the required input force by increasing the distance.

   A ramp does not change the amount of gravitational work needed to raise an object; it only spreads that work over a longer distance, allowing a smaller input force. Therefore the task feels easier because the required force is reduced, not because the work or gravity changes.

6. Question 6

   What is the ratio of output force to input force for a simple machine called?
   • AWork input
   • BPower
   • CEfficiency
   • DMechanical advantage
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   Answer: D) Mechanical advantage

   Mechanical advantage is defined as the ratio of the output force produced by a simple machine to the input force applied to it. This directly answers the question. Efficiency, power, and work input refer to different concepts: efficiency relates output work to input work, power is the rate of doing work, and work input is the total energy supplied, not a force ratio.

7. Question 7

   Which simple machine consists of an inclined plane wrapped around a central cylinder?
   • AWedge
   • BScrew
   • CPulley
   • DLever
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   Answer: B) Screw

   A screw is defined as an inclined plane that is wrapped around a central cylinder, forming a helical thread. This matches the description in the stem. The other options describe different simple machines: a wedge is two inclined planes placed back‑to‑back, a pulley is a grooved wheel with a rope, and a lever is a rigid bar rotating about a fulcrum. None of these involve a wrapped inclined plane.

8. Question 8

   A pair of scissors and a nutcracker are both simple machines using levers. How do their structural arrangements differ?
   • AScissors have the fulcrum between effort and load, while nutcrackers have the load between fulcrum and effort.
   • BScissors have the load between fulcrum and effort, while nutcrackers have the fulcrum in the middle.
   • CScissors have the effort between fulcrum and load, while nutcrackers have the fulcrum in the middle.
   • DScissors and nutcrackers both have the effort located directly between the fulcrum and load.
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   Answer: A) Scissors have the fulcrum between effort and load, while nutcrackers have the load between fulcrum and effort.

   Scissors have the fulcrum (the pivot) between the effort applied at the handles and the load at the cutting blades, making them first‑class levers. Nutcrackers place the nut (load) between the fulcrum (the hinge) and the effort applied on the handles, which is the definition of a second‑class lever. The other options reverse or misclassify these arrangements.

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