A weightlifter lifts a bar with mass of 10 kg fixed on each side of bar. Class 9

A weightlifter lifts a bar with mass of 10 kg fixed on each side of bar. Class 9

Question 1.

A weightlifter lifts a bar with mass of 10 kg fixed on each side of bar. The mass of bar is 10 kg. How much force is he applying to keep the bar steady? Class 9

Answer:

Total mass of bar of 10 kg with 10 kg mass fixed on each side = 10 + 10 + 10 = 30 kg Gravitational force acting on bar in downward direction is F = mg = 30 × 9.8 = 294 N To keep the bar steady, weightlifter has to apply equal force in opposite direction = 294 N in upward direction

Question 2.

Ramesh is pushing stationary object of 25 kg on floor. Force of friction opposing this motion is 50 N. What is the displacement of object in 2 s if he pushes it with constant force of : Class 9

(i) 50 N and

(ii) 55 N in the forward direction.

Answer:

(i) 50 N applied force = 50 N force of friction opposing the motion. Net force acting on stationary object = 0. Therefore, object will remain stationary.

(ii) Net force acting on stationary object = 55 - 50 = 5 N.

F = ma

5 = 25 a

a = 0.2 m/s²

Displacement in 2 seconds in forward direction is

s = ut + 1/2 at²

= 0 + 1/2 × 0.2 × 2 × 2 = 0.4 m

F = ma

= 0.04 × 6750

= 270 N