Laws and levers / laws of moments

Back to: PRIMARY SEVEN P7 SCIENCE TOPICAL QUESTIONS AND ANSWERS

Laws and levers / laws of moments
Qn. State the law of levers / law of moments.

• The law of levers states that load force multiplied by the load arm is equal to the effort force multiplied by the effort arm.
  OR
• The law of levers states that the sum of the clockwise moments about any point is equal to the sum of anticlockwise moments. i.e.

Load X load arm = Effort X Effort arm

L X LA = E X EA

Qn. What is a moment?

• A moment is a turning force of a machine.
  Calculations on levers

1. James who weighs 60kgf sits 2m away from the fulcrum and balances with Joan who weigh 30kg from a see saw. How far from the fulcrum does Joan sit?
   Solution

Joan sits 4 metres away from the fulcrum.
Let the effort arm be K.

2. Annet is 35kg, if she sits 2cm away from the fulcrum and balances with Opio who sits 5cm away from the fulcrum, what is Opio’s weight?
   Solution
   

Opio’s weight is 14kg

4. Moses is 50kg. He sits 4m away from the fulcrum to balance with Jane who wighs 25kgs on a see saw. How far is Jane from Musa?

Activity:

1. Charity weighs 90kgf. If she sits 3m away from the pivot of a see saw, how far Joel whose weight is 30kgf will sit in order to balance.
2. Darius weighs 50kg andsits 4m away from the fulcrum. Regina weighs 40kg. How far from the fulcrum will Regina sit in order to balance with Darius.
   b) How far will Regina be from Darius?
3. John and Jane sat on a see saw as shown below.