Q: 1 joule is defined as the work done when?
Answer: A 1 N force moves a body by 1 m in its direction
Explanation: Joule is defined using force and displacement. 1 joule is the work done by 1 newton through 1 meter along the force. This links energy directly to mechanical work.
Q: Work done by a variable force is equal to?
Answer: Area under the force–displacement graph
Explanation: When force varies with displacement, work is found by integrating force over distance. Graphically, this equals the area under the F–x curve. This idea is used in springs and non-uniform forces.
Q: Convert 36 km/h into m/s.?
Answer: 10 m/s
Explanation: To convert km/h to m/s, divide by 3.6. So 36/3.6 = 10 m/s. This conversion is often used in motion and energy problems.
Q: What is the kinetic energy of a 10 kg body moving with speed 2 m/s?
Answer: 20 J
Explanation: Use KE = (1/2)mv^2 with m = 10 and v = 2. So KE = (1/2) x 10 x 4 = 20 J. Kinetic energy depends on the square of speed.
Q: Gravitational potential energy near Earth’s surface is given by?
Answer: PE = mgh
Explanation: Near Earth’s surface, potential energy depends on height in a uniform gravitational field. The expression is PE = mgh for mass m raised by height h. It increases linearly with both m and h.
Q: How much work is needed to raise a 2 kg mass by 10 m? (Take g = 10 m/s^2)?
Answer: 200 J
Explanation: Work against gravity equals W = mgh. Here W = 2 x 10 x 10 = 200 J. This work becomes the body’s gravitational potential energy.
Q: In a simple pendulum, at the mean (lowest) position, the bob has?
Answer: Maximum kinetic energy
Explanation: At the lowest point, height is minimum so potential energy is minimum. Speed is maximum there, so kinetic energy is maximum. Total mechanical energy remains constant if no losses act.
Q: The efficiency of any machine can never be greater than?
Answer: 100%
Explanation: Efficiency compares useful output to input, so it cannot exceed the input. Due to unavoidable losses, real machines have efficiency less than 100%. 100% efficiency is an ideal limit.
Q: Elastic potential energy stored in a spring is proportional to?
Answer: Square of extension
Explanation: Spring energy depends on extension as (1/2)kx^2. This means it is proportional to the square of extension x. Doubling x makes the stored energy four times.
Q: A 100 W bulb glows for 10 hours. How much energy is used in kWh?
Answer: 1 kWh
Explanation: Convert 100 W to kW: 100 W = 0.1 kW. Energy = power x time = 0.1 x 10 = 1 kWh. kWh is a practical unit for electrical energy usage.