Question 1
The work done by the weight of a 1 Kg mass while it moves up through 1 m is:
- a. 9.8 J
- b. -9.8 J
- c. 1/9.8 J
- d. -1/9.8 J
Question 2
A force of 10 N acts on a body towards the east. Work done by the force while the body moves through 1 m in east-north direction (midway between east and north) is:
- a. 10√2 J
- b. 10/√2 J
- c. -10 J
- d. -10/√2 J
Question 3
When a stone tied to a string is whirled in a circle, the work done on it by the string is:
- a. Positive
- b. Negative
- c. Zero
- d. Undefined
Question 4
A body of mass 2 Kg is dropped from a height of 1 m. Its kinetic energy as it reaches the ground is:
- a. 19.6 J
- b. 19.6 N
- c. 19.6 Kg
- d. 19.6 m
Question 5
A person A does 500 J of work in 10 minutes and another person B does 600 J of work in 20 minutes. Let the power delivered by A and B be P1 and P2 respectively then,
- a. P1 = P2
- b. P1 > P2
- c. P1 < P2
- d. P1 and P2 are undefined
Question 6
A car is accelerated on a leveled road and acquires a velocity of 4 times its initial velocity. During the process, the potential energy of the car:
- a. Does not change
- b. Becomes twice that of initial potential energy
- c. Becomes 4 times that of initial potential energy
- d. Becomes 16 times that of initial potential energy
Question 7
An object is falling freely from a height of x. After it has fallen a height of x/2, it will possess:
- a. Only potential energy
- b. Only kinetic energy
- c. Half potential energy and half kinetic energy
- d. Less potential energy and more kinetic energy
Question 8
An electric motor raises a load of 0.2 Kg at a constant speed, through a vertical distance of 3.0 m in 2 seconds. If the acceleration of free fall is 10 m/s^2, the power in watt developed by the motor in raising the load is:
- a. 0.3
- b. 1.2
- c. 3.0
- d. 6.0
Question 9
Which of the following is not the unit of energy?
- a. Joule
- b. Newton-meter
- c. Kilowatt
- d. Kilowatt-hour
Question 10
How much energy does a 100-watt electric bulb transfer in 1 minute?
- a. 100 J
- b. 600 J
- c. 3600 J
- d. 6000 J
Solutions
Question 1
The work done by the weight of a 1 Kg mass while it moves up through 1 m is:
Solution
The work done is negative because the direction of force is opposite to the direction of displacement.
[
W = F times d times cos(180^circ) = -9.8 , text{J}
]
Answer: b. -9.8 J
Question 2
A force of 10 N acts on a body towards the east. Work done by the force while the body moves through 1 m in east-north direction is:
Solution
The angle between the force and the direction of motion is ( 45^circ ).
[
W = F times d times cos(45^circ) = 10 times frac{1}{sqrt{2}} , text{J}
]
Answer: b. ( 10/sqrt{2} , text{J} )
Question 3
When a stone tied to a string is whirled in a circle, the work done on it by the string is:
Solution
The stone moves in a direction perpendicular to the force, so no work is done.
Answer: c. Zero
Question 4
A body of mass 2 Kg is dropped from a height of 1 m. Its kinetic energy as it reaches the ground is:
Solution
The kinetic energy is given by ( KE = m times g times h ).
[
KE = 2 , text{Kg} times 9.8 , text{m/s}^2 times 1 , text{m} = 19.6 , text{J}
]
Answer: a. 19.6 J
Question 5
A person A does 500 J of work in 10 minutes and another person B does 600 J of work in 20 minutes. Let the power delivered by A and B be ( P_1 ) and ( P_2 ) respectively.
Solution
Power is given by ( P = frac{W}{t} ).
[
P_1 = frac{500 , text{J}}{600 , text{s}} quad text{and} quad P_2 = frac{600 , text{J}}{1200 , text{s}}
]
[
P_1 = P_2
]
Answer: a. ( P_1 = P_2 )
Question 6
A car is accelerated on a leveled road and acquires a velocity of 4 times its initial velocity. During this process, the potential energy of the car:
Solution
Since the car is on a leveled road, its height doesn’t change. Therefore, its potential energy remains the same.
Answer: a. Does not change
Question 7
An object is falling freely from a height of ( x ). After it has fallen a height of ( x/2 ), it will possess:
Solution
When the object has fallen ( x/2 ), it has converted some of its initial potential energy into kinetic energy. Therefore, it has both kinetic and potential energy.
Answer: c. Half potential energy and half kinetic energy
Question 8
An electric motor raises a load of 0.2 Kg at a constant speed, through a vertical distance of 3.0 m in 2 seconds. If the acceleration of free fall is ( 10 , text{m/s}^2 ), the power in watt developed by the motor in raising the load is:
Solution
Power ( P = frac{W}{t} )
Work ( W = F times d )
[
F = m times g = 0.2 times 10 = 2 , text{N}, quad d = 3 , text{m}
]
[
P = frac{2 times 3}{2} = 3 , text{W}
]
Answer: c. 3.0
Question 9
Which of the following is not the unit of energy?
Solution
Kilowatt is a unit of power, not energy.
Answer: c. Kilowatt
Question 10
How much energy does a 100-watt electric bulb transfer in 1 minute?
Solution
Energy ( E = P times t )
[
E = 100 , text{W} times 60 , text{s} = 6000 , text{J}
]
Answer: d. 6000 J