NCERT Solutions for Class 9th Science Chapter 6 .2 Balanced and Unbalanced Forces — Pause and Ponder
Book page 976 Updated on2026-09-08
Q1.
A weightlifter lifts a barbell (Fig. 6.8). List two forces that are acting on the barbell. Are these forces balanced if the weightlifter keeps the barbell steady?
Answer
The two forces on the barbell are:
The gravitational force (weight) of the barbell, exerted by the Earth, acting vertically downwards.
The upward force applied by the weightlifter's hands on the bar.
Yes — while she holds it steady, the two forces are balanced.
Why it happens: "steady" means the barbell is at rest, so its velocity is not changing and its acceleration is zero. By Newton's second law, a = F/m, zero acceleration for a non-zero mass requires the net force to be zero. Hence the upward push of her hands must exactly equal the downward weight.
Forces on a barbell held steady: equal in magnitude, opposite in direction, so they balance.
Did you know? Example 6.4 works out the number: a 30 kg barbell needs F = mg = 30 kg × 9.8 m s–2 = 294 N upwards.
Q2.
Two players R and S are participating in an arm-wrestling match (Fig. 6.9). At the instant, when the arms tilt to the front direction (out of the page towards you), are the forces exerted by the players balanced? If not, which player exerted the larger force?
Answer
No, the forces are not balanced at that instant. Player R exerted the larger force.
Why it happens: the joined hands only stay still while the two pushes are equal and opposite — balanced. The moment the hands actually move, the velocity has changed from zero to something, so there is an acceleration and therefore a non-zero net force. The net force, and hence the motion, is along the direction of the larger force. In Fig. 6.9, R is on the left of the picture and the arms tilt out of the page towards you — that is R's pushing direction, so R is pushing harder.
Tip: "the arms have not moved yet" is the balanced case; "the arms are moving" is always the unbalanced case. Look at the direction of the movement — it tells you whose force is bigger.