BMST Work, Energy, and Power — Questions and Answers
Question 1: How much work is done when a force of 50 N moves an object 8 meters in the direction of the force?
- 400 J (Correct answer)
- 58 J
- 6.25 J
- 40 J
Correct answer: 400 J
Work = Force × Distance = 50 N × 8 m = 400 Joules. Work is only done when the force has a component in the direction of motion.
Question 2: A 2 kg ball is moving at 6 m/s. What is its kinetic energy?
- 36 J (Correct answer)
- 12 J
- 72 J
- 6 J
Correct answer: 36 J
Kinetic Energy = ½mv² = ½ × 2 × (6)² = ½ × 2 × 36 = 36 J.
Question 3: An object with a mass of 5 kg is lifted 3 meters above the ground. What is its gravitational potential energy? (g = 10 m/s²)
- 150 J (Correct answer)
- 50 J
- 15 J
- 300 J
Correct answer: 150 J
Potential Energy = mgh = 5 kg × 10 m/s² × 3 m = 150 J.
Question 4: A machine does 500 J of work in 10 seconds. What is its power output?
- 50 W (Correct answer)
- 5000 W
- 500 W
- 0.02 W
Correct answer: 50 W
Power = Work / Time = 500 J / 10 s = 50 Watts. Power measures the rate at which work is done.
Question 5: According to the work-energy theorem, if a net force does 200 J of work on an object, what happens to the object's kinetic energy?
- It increases by 200 J (Correct answer)
- It decreases by 200 J
- It stays the same
- It doubles
Correct answer: It increases by 200 J
The work-energy theorem states that net work done on an object equals the change in its kinetic energy. Positive net work increases kinetic energy.
Question 6: A 10 kg object falls from a height of 5 m. Ignoring air resistance, what is its kinetic energy just before it hits the ground? (g = 10 m/s²)
- 500 J (Correct answer)
- 50 J
- 250 J
- 1000 J
Correct answer: 500 J
All potential energy converts to kinetic energy: KE = mgh = 10 × 10 × 5 = 500 J. This demonstrates conservation of mechanical energy.
BMST Work, Energy, and Power
How much work is done when a force of 50 N moves an object 8 meters in the direction of the force?