This quiz explores core principles of work, energy, and power with practical scenarios and carefully constructed questions. Ideal for students and enthusiasts aiming to reinforce their understanding through realistic examples and application-based problems.
If a student pushes a box with a constant force of 20 newtons over a distance of 5 meters in the direction of the force, what is the total work done on the box?
Explanation: Work is calculated using the formula: Work = Force × Distance × cos(theta). Since the force and motion are in the same direction, cos(theta) is 1, so 20 newtons × 5 meters = 100 joules. 25 joules and 4 joules result from multiplying with incorrect values or using the wrong formula, while 15 newtons is a force unit, not work. Only 100 joules matches both the correct calculation and units for work.
At the top of a roller coaster, a cart has a potential energy of 2000 joules. Assuming no energy is lost, what will its kinetic energy be just before it reaches the bottom?
Explanation: Under the law of conservation of energy, all potential energy is converted to kinetic energy if there are no losses, so it becomes 2000 joules. 0 joules is incorrect as the cart gains speed. 1000 and 2500 joules do not conserve the total starting energy or invent energy beyond what’s provided. The correct answer is 2000 joules.
Which of the following units is the standard unit of power in the International System (SI)?
Explanation: The watt is the SI unit for power, measuring the rate of doing work (joules per second). Joule is a unit of energy, not power. Newton is a unit for force, and pascal is for pressure. Only watt directly measures power according to the SI system.
If a pulley lifts a 50 kg object by 2 meters using 1200 joules of input energy, what is the efficiency of the system? (Take g = 10 m/s².)
Explanation: Efficiency is output energy divided by input energy, times 100. Output work = m × g × h = 50×10×2 = 1000 joules. Efficiency = (1000/1200)×100 ≈ 83.3%. 100% assumes no energy is lost, which isn’t the case here. 50% is too low, and 120% is impossible because efficiency can't exceed 100%. Thus, 83.3% is correct.
A person attempts to hold back a moving sled, applying a force opposite to its motion, causing it to slow down. What type of work is the person doing on the sled?
Explanation: Work is negative when the applied force acts in the opposite direction of motion, which slows the object. Zero work happens when there’s no displacement or force is perpendicular to motion, neither of which apply here. Positive work would mean force and motion are in the same direction. Non-mechanical work is not relevant to this scenario.