NCERT Solutions for Class 9th Science Chapter 7 .6.3 Lever — In-text Questions
Book page 1337 Updated on2026-09-08
Q1.
By applying a small force at one end of the lever, a larger force can be applied on the object on the other end of the lever. How is this possible?
Answer
It is possible because the lever passes on the work, not the force. The end you press moves through a large distance with a small force; the load end moves a small distance with a large force.
A small effort moving through a long arm delivers a large force through a short arm: F₁ × d₁ = F₂ × d₂.
Work put in at the effort end = work delivered at the load end F1 × d1 = F2 × d2 (Eq. 7.14)
Rearranging: F2 = F1 × (d1 / d2)
Mechanical advantage = effort arm / load arm = d1 / d2 (Eq. 7.16)
Why it happens: the lever is a rigid bar turning about the fulcrum, so both ends turn through the same angle in the same time. The end further from the fulcrum must therefore travel a proportionally longer arc. Since the work done on the bar at one end reappears at the other, a longer path must go with a smaller force, and a shorter path with a larger one.
What a lever cannot do: it does not reduce the total work, and it does not create energy. Lift a 200 N rock by 0.1 m and you must supply 20 J, whether you use a crowbar or your bare hands.