Exercise 6.1
A weightlifter lifts a barbell (Fig. ). List two forces that are acting on the barbell. Are these forces balanced if the weightlifter keeps the barbell steady?
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
The two forces on the barbell are the gravitational force (its weight), acting downwards, and the upward force applied by the weightlifter's hands.
Yes — if the barbell is held steady, these two forces are balanced.
Steady means the barbell is at rest: its velocity is zero and unchanging, so by Newton's first law the net force on it must be zero.
Two forces balance when they are equal in magnitude and opposite in direction, so the lifter's upward push exactly equals the weight.
For the barbell of Example $\displaystyle 6.4$ (total mass $\displaystyle 30$ kg), the weight is \(\displaystyle F = mg = 30\ \text{kg} \times 9.8\ \text{m s}^{-2} = 294\ \text{N} \) downwards, so the lifter applies \(\displaystyle 294\ \text{N} \) upwards.