**Hint:** Judge situations to identify where work is done according to scientific conception and calculate the magnitude of work.

**Question.1.** Which of these is an example of scientific work done?

(a) Standing with a load of 2 kg on the head for 5 minutes

(b) Playing video games when sitting on a sofa

(c) Sitting on a chair and reading a book

(d) Climbing stairs of a bridge

**Question.2.** A force of 20 N acts on an object. It causes a displacement of 500 cm in the direction of force. What would be the work done in Nm on the object?

(a) 1000

(b) 100

(c) 25

(d) 4

**Ans.1.** (d) Climbing stairs of a bridge**Ans.2.** (b) 100

**Hint:** Calculate the total work done on an object when force is applied in varied directions and determine its nature.

**Question.3.** A boy pushes a lawn mower to a total distance of 125 m over the grass with a force of 60 N directed horizontally. How much work is done in joules by the boy?

(a) +7500

(b) -7500

(c) +2.03

(d) -2.03

**Question.4.** An object is moving with a uniform velocity along a particular direction. A retarding force of 5 N, is applied in the direction as shown. The object stops after a displacement of 5 m. What is the work done by the retarding force?

(a) -5 J

(b) -25 J

(c) 5 J

(d) 25 J

**Ans.3.** (a) +7500**Ans.4.** (b) -25 J

**Hint:** Comprehend energy and calculate the amount of work an object is capable of doing.

**Question.5.** An object of mass 25 kg is at a height of 8 m above the ground. How much work is this object capable of doing? Given g = 9.8 ms^{-2}.

(a) 1960 J

(b) 2000 J

(c) 19600 J

(d) 20000 J

**Question.6.** The kinetic energy of an object weighing 10 kg moving with a velocity of 5 m/s is 125 J. What is the maximum amount of work that can be done by the object?

(a) 5 J

(b) 10 J

(c) 125 J

(d) 1250 J

**Ans.5.** (a) 1960 J **Ans.6.** (c) 125 J

**Hint:** Relate kinetic energy to motion and calculate kinetic energy possessed by the objects.

**Question.7.** What would be the kinetic energy possessed by an object of mass, ‘2m’ and moving with a uniform velocity, ‘v’?

(a) \frac{1}{2}mv^{2}

(b) mv^{2}

(c) 2mv^{2}

(d) 4mv^{2}

**Question.8.** A car weighing 500 kg is moving with a uniform velocity of 15 m/s. What is the kinetic energy possessed by the car?

(a) 56.250 kJ

(b) 112.500 kJ

(c) 56250 kJ

(d) 112500 kJ

**Ans.7.** (b) mv^{2}**Ans.8.** (a) 56.250 kJ

**Hint:** Comprehend energy transfer and write an expression for the kinetic energy of an object.

**Question.9.** An object of mass 200 g moving with velocity 50 m/s. What is its kinetic energy?

(a) 2.1\times 10^{5} J

(b) 2.0\times 10^{5} J

(c) 2.8\times 10^{5} J

(d) 2.5\times 10^{5} J

**Question.10.** A particle is thrown upward with some kinetic energy. What happened to its kinetic energy at the highest point or height it reaches?

(a) Its kinetic energy is lost;

(b) It’s all kinetic energy is absorbed by the air;

(c) Its kinetic energy is converted to potential energy;

(d) Its kinetic energy is remain same;

**Ans.9.** (d) 2.5\times 10^{5} J**Ans.10.** (c) Its kinetic energy is converted to potential energy

**Hint:** Relate potential energy to position and calculate potential energy possessed by the objects.

**Question.11.** An object of mass ‘x’ kg is placed on the surface of Earth. What is the energy possessed by the object by the virtue of its position? Given g = 9.8 ms^{-2}.

(a) -9.8x J

(b) 0 J

(c) 9.8x J

(d) \frac{x}{2} J

**Question.12.** Compare the energy possessed by the virtue of position for the 2 bodies shown below.

(a) By virtue of their positions, the energy possessed by body A is half the energy possessed by body B.

(b) By virtue of their positions, the energy possessed by body A is twice the energy possessed by body B.

(c) By virtue of their positions, the energy possessed by body A is 4 times the energy possessed by body B.

(d) By virtue of their positions, the energy possessed by both Body A and Body B is the same.

**Ans.11.** (b) 0 J**Ans.12.** (b) By virtue of their positions, the energy possessed by body A is twice the energy possessed by body B.

**Hint:** Generalise the law of conservation of energy to situations of energy transfer and calculate the total energy of an object.

**Question.13.** A 50 kg skydiver jumps from a height of 20 m. What would be his kinetic and potential energies when he is halfway down? Assume g = 10 ms^{-2}.

(a) KE = 5,000 J; PE = 5,000 J

(b) KE = 0 J; PE = 10,000 J

(c) KE = 10,000 J; PE = 0 J

(d) KE = 10,000 J; PE = 10,000 J

**Question.14.** Refer to the image below.Which option correctly compares the KE and PE of the ball in the stages A, B and C?

(a) (b) (c) (d)

**Ans.13.** (a) KE = 5,000 J; PE = 5,000 J **Ans.14.** (c)

**Hint:** Calculate power and assess the efficiency of work done.

**Question.15.** The power expended by 4 persons to do a task is shown in the table below.Who performed the task most efficiently?

(a) A

(b) B

(c) C

(d) D

**Question.16.** A man of mass is 60 kg climbs up 50 steps of a stair in 2 minutes. If each step is 20 cm high, calculate the power used in climbing the stairs. [Given g = 10 ms^{-2}]

(a) 50 W

(b) 250 W

(c) 3000 W

(d) 6000 W

**Ans.15.** (d) D**Ans.16.** (a) 50 W

**Hint:** Get conversant with commercial unit of energy.

**Question.17.** A machine do a work of 100 joule in 20 second. What is its power?

(a) 20 watt

(b) 80 watt

(c) 5 watt

(d) 2000 watt

**Question.18.** Which of the following is equal with Newton-meter?

(a) Joule

(b) Horse Power

(c) Watt

(d) Pascal

**Ans.17.** (c) 5 watt**Ans.18.** (a) Joule

**Hint:** Calculate total energy consumption and determine total cost in households and industries.

**Question.19.** A factory has eight machines of 1200 W each. If each machine runs for 10 hours a day, find the cost of electrical units’ consumption per day if the rate per unit is 4.00 rupees?

(a) 96 rupees

(b) 120 rupees

(c) 384 rupees

(d) 3840 rupees

**Question.20.** A household has four bulbs of 100 W each. If the bulbs operate for 10 hours daily, find the monthly expenditure incurred? (Cost of 1 unit = 2.50 rupees)

(a) Rs 75

(b) Rs 250

(c) Rs 300

(d) Rs 2500

**Ans.19.** (c) 384 rupees**Ans.20.** (c) Rs 300