Work and Its Types - UNSOLVED PRACTICE SET

Q7. Define work in scientific terms. Write the formula and explain the role of the angle between force and displacement.

Q8. Give one example each of:
(a) positive work,
(b) negative work, and
(c) zero work.
For each, identify the force and the direction of displacement.

Q9. A person pushes a wall with great effort for 10 minutes but the wall does not move. Has the person done any work according to Physics? Explain clearly.

Q10. A satellite revolves around the Earth in a circular orbit. The gravitational force acts towards the centre of Earth. How much work does gravity do on the satellite in one complete revolution? Justify.

Q11. What is meant by 'work done against gravity'? A student picks up her school bag of mass 5 kg from the floor and places it on a table 0.8 m high. Calculate the work done against gravity. (g = 10 m/s²)

Q12. Distinguish between positive work and negative work. When a car brakes to a stop, is the work done by friction positive or negative? Explain.

Q13. Explain the scientific definition of work with reference to force, displacement, and angle. Your answer must cover:
(a) the formula W = F·s·cosθ and what each symbol means,
(b) the three cases — θ = 0°, θ = 90°, θ = 180° — with one real-life Indian example for each,
(c) why the coolie carrying a bag on a level platform does zero work against gravity even though he is exerting effort, and
(d) what is 1 Joule of work.

Q14. A construction worker in Mumbai lifts bricks repeatedly from the ground to a scaffold 3 m high. Each brick has a mass of 2 kg.
(a) Calculate the work done in lifting one brick (g = 10 m/s²).
(b) If he lifts 40 bricks in one hour, what is the total work done?
(c) If a crane does the same job in 5 minutes, has the crane done the same work?
(d) What is the difference between what the worker did and what the crane did? Name the physical quantity that captures this difference.
(e) Explain whether the work done depends on how long it takes.

Q15. Analyse each of the following situations and calculate the work done, stating whether it is positive, negative, or zero:
(a) A horse pulls a cart with 500 N of force across 2 km on a level road.
(b) A child carries a 4 kg bag at the same height across 100 m.
(c) A spring is compressed by 0.05 m with a force of 200 N.
(d) A stone of mass 1 kg falls freely through 5 m (g = 10 m/s²).
(e) A block slides 3 m on a surface against a friction force of 15 N.

Q16. A farmer in Punjab pushes a plough with a force of 200 N at an angle of 30° to the ground, covering a field 50 m long.
(a) Write the formula for work when force is at an angle.
(b) Calculate the work done by the farmer.
(c) If the farmer had pushed horizontally (0°) with the same force, how much work would have been done?
(d) Which gives more work and why? (cos 30° = 0.866)

Q17. A rickshaw puller in Varanasi exerts a force of 150 N to pull a rickshaw. In the first 200 m, he pulls it forward (positive work). He then brakes, and a friction force of 80 N acts over the next 50 m (negative work).
(a) Calculate the positive work done.
(b) Calculate the work done by friction.
(c) Calculate the net work done on the rickshaw.

Q18. A box of mass 12 kg is dragged along a rough floor for 6 m. The applied force is 90 N horizontally. Friction force is 30 N opposing motion.
(a) Calculate work done by applied force.
(b) Calculate work done by friction (negative).
(c) Calculate work done by gravity.
(d) Calculate the net (total) work done on the box.
(e) Using the Work-Energy Theorem (net work = change in KE), find the final KE if the box started from rest.