← Back to Science Chapters
Ch-11: Work and Energy
10 Questions
Before You Practice Try each question on your own first. Use the Show Answer button only after you have selected your option, then read the explanation and revise the related concept from your chapter notes.
1. Work is said to be done on an object when:
A. A force acts on it without moving it
B. A force acts on it and causes displacement in the direction of force
C. The object moves without any applied force
D. Force and displacement are perpendicular to each other
Show Answer
Answer: B. A force acts on it and causes displacement in the direction of force
Explanation: Work (W = F × s) requires both an applied force and a non-zero displacement in the direction of the force.
2. What is the SI unit of Work and Energy?
A. Watt
B. Newton
C. Joule
D. Pascal
Show Answer
Answer: C. Joule
Explanation: Both work and energy are measured in Joules (J). 1 Joule = 1 Newton × 1 meter.
3. When the force applied on a body is perpendicular to its direction of motion, the work done is:
A. Positive
B. Negative
C. Maximum
D. Zero
Show Answer
Answer: D. Zero
Explanation: W = F × s × cos(θ). When angle θ = 90°, cos(90°) = 0, so work done is zero (e.g., a coolie carrying a load walking horizontally).
4. Kinetic Energy of an object of mass m moving with velocity v is given by the formula:
A. mgh
B. ½ mv²
C. mv²
D. ½ m²v
Show Answer
Answer: B. ½ mv²
Explanation: Kinetic energy possesses by a moving body is proportional to its mass and the square of its velocity (E_k = ½ mv²).
5. Gravitational potential energy of an object raised to a height h is equal to:
A. mgh
B. ½ mgh
C. mg / h
D. m / gh
Show Answer
Answer: A. mgh
Explanation: Work done against gravity to raise an object to height h is W = F × h = (mg) × h = mgh, stored as potential energy.
6. According to the Law of Conservation of Energy, energy can neither be created nor destroyed; it can only be:
A. Increased
B. Transformed from one form to another
C. Completely eliminated
D. Decreased
Show Answer
Answer: B. Transformed from one form to another
Explanation: The total mechanical energy (Potential Energy + Kinetic Energy) remains constant during energy transformations in an isolated system.
7. What is Power defined as?
A. Force per unit area
B. Rate of doing work (or rate of energy consumption)
C. Product of force and velocity
D. Energy multiplied by time
Show Answer
Answer: B. Rate of doing work (or rate of energy consumption)
Explanation: Power = Work / Time (P = W / t). Its SI unit is Watt (W), where 1 Watt = 1 Joule/second.
8. What is the commercial unit of electrical energy?
A. Joule (J)
B. Watt-hour (Wh)
C. Kilowatt-hour (kWh)
D. Megawatt (MW)
Show Answer
Answer: C. Kilowatt-hour (kWh)
Explanation: 1 unit of electricity equals 1 kWh. It represents energy consumed by a 1 kW appliance running for 1 hour.
9. How many Joules are there in 1 Kilowatt-hour (1 kWh)?
A. 3.6 × 10⁵ J
B. 3.6 × 10⁶ J
C. 36 × 10⁶ J
D. 1000 J
Show Answer
Answer: B. 3.6 × 10⁶ J
Explanation: 1 kWh = 1000 W × 3600 s = 3,600,000 Joules = 3.6 × 10⁶ J.
10. An electric bulb of 60 W is used for 5 hours per day. Calculate the energy consumed in one day in units (kWh).
A. 0.3 units
B. 3 units
C. 0.03 units
D. 300 units
Show Answer
Answer: A. 0.3 units
Explanation: Power = 60 W = 0.06 kW. Time = 5 h. Energy = Power × Time = 0.06 kW × 5 h = 0.3 kWh (0.3 units).
