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Levers & Pulleys Worksheet

Class 9 & 10 · Simple machines · about 40 minutes · open the simulation at jugnix.com/simulations/levers-pulleys

NameClassDate

By the end you will: find mechanical advantage and velocity ratio for levers and pulleys, and explain why no machine saves work.

A. Explore with the simulation

  1. Choose Lever, Class 1 and the Rice sack (50 kg, 490 N). Move the fulcrum and record the effort needed.

    Fulcrum atEffort arm : load armMechanical advantageEffort needed (N)
    1.00 m
    2.00 m
    3.00 m

  2. Switch to Class 3 with the effort at 1.00 m. What is the mechanical advantage? Why would anyone use a lever like this?

  3. Choose Pulley, the Cow (500 kg), and each pulley system. Record the pull needed.

    Pulley systemPull needed (N)
    1 fixed pulley
    1 movable pulley
    4 ropes
    6 ropes

  4. With 4 ropes, pull 2 m of rope. How high does the load rise? Compare the work you do with the work done on the load.

B. Calculate (then check in the simulation)

  1. A 20 kg child sits 1.5 m from the pivot of a seesaw. Where must a 30 kg child sit to balance?

  2. A wheelbarrow carries 600 N, 0.4 m from the wheel. You lift the handles 1.2 m from the wheel. What effort do you need?

  3. A pulley system with a velocity ratio of 5 lifts 1,000 N with an effort of 250 N. Find the mechanical advantage and the efficiency.

C. Think it through

  1. Name the class of lever: scissors, nutcracker, tweezers, bottle opener, see-saw, your forearm.

Answer key (for teachers and parents)

  1. 1 m: arms 3 : 1, MA 3, 163 N · 2 m: arms 2 : 2, MA 1, 490 N · 3 m: arms 1 : 3, MA 0.33, 1,470 N. The closer the fulcrum is to the load, the less effort you need.
  2. MA = 0.25: you need 4 times the load's weight. But the load end moves 4 times as far and as fast, which is useful in tweezers, fishing rods and your forearm.
  3. 1 fixed: 4,900 N · 1 movable: 2,450 N · 4 ropes: 1,225 N · 6 ropes: 817 N. Pull = load ÷ number of ropes holding it.
  4. It rises 0.5 m. Your work = 1,225 N × 2 m = 2,450 J; work on the load = 4,900 N × 0.5 m = 2,450 J. The same: the machine saves force, not work.
  5. 20 × 1.5 = 30 × d, so d = 1 m.
  6. Effort × 1.2 = 600 × 0.4, so effort = 200 N. MA = 3.
  7. MA = 1,000 ÷ 250 = 4. Efficiency = MA ÷ VR = 4 ÷ 5 = 80%.
  8. Class 1: scissors, see-saw. Class 2: nutcracker, bottle opener. Class 3: tweezers, forearm.

Free to print and share for teaching. Made with the interactive simulation at jugnix.com/simulations/levers-pulleys.