Practice using force and work concepts to understand how simple machines make tasks easier.
Read each problem carefully. Show your work in the space provided. Include units in your answers when numbers are given.
Exploring force, work, mechanical advantage, and simple machines
Physics - Grade 6-8
- 1
A student pushes a box with a force of 40 newtons, but the box does not move. How much work is done on the box? Explain your answer.
- 2
A wagon is pulled with a force of 25 newtons for a distance of 6 meters. How much work is done on the wagon?
- 3
A ramp helps a worker move a heavy box into a truck. Explain how the ramp makes the job easier, even though the box must be moved a longer distance.
- 4
A simple machine has an input force of 20 newtons and produces an output force of 80 newtons. What is the mechanical advantage of the machine?
- 5
Classify each tool as a lever, pulley, wheel and axle, inclined plane, wedge, or screw: scissors, flagpole rope system, doorknob, knife, and jar lid.
- 6
A lever has a fulcrum in the middle, an input force on one end, and a load on the other end. What class of lever is it? Give one example.
- 7
A student lifts a 60-newton backpack straight up 1.5 meters. How much work is done on the backpack?
- 8
A machine has a mechanical advantage of 3. If the input force is 50 newtons, what output force does the machine produce?
- 9
Two students move identical boxes onto the same stage. Student A lifts a box straight up 1 meter. Student B pushes a box up a ramp that is 4 meters long. Compare the force each student must use and the work done in an ideal situation.
- 10
A pulley system changes the direction of a force so a person can pull down on a rope to lift a bucket up. Does this pulley system always reduce the amount of input force needed? Explain.
- 11
A machine does 200 joules of useful output work when 250 joules of input work are put into it. What is the efficiency of the machine?
- 12
Why is the efficiency of a real machine usually less than 100 percent?
- 13
A screw is used to hold two pieces of wood together. Explain how a screw is related to an inclined plane.
- 14
A person uses a crowbar to pry open a lid. The fulcrum is placed close to the lid. Why does this make the crowbar more helpful?
- 15
A wheelbarrow has the wheel as the fulcrum, the load in the bucket, and the effort applied at the handles. What class of lever is a wheelbarrow, and how does it help the user?