Work, Energy & Power
Q. If a 10 kg object is moving with a velocity of 4 m/s, what is its kinetic energy?
A.
80 J
B.
40 J
C.
20 J
D.
160 J
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Solution
Kinetic Energy (KE) = 1/2 * m * v^2 = 1/2 * 10 * (4^2) = 80 J
Correct Answer: A — 80 J
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Q. If a 1000 kg car accelerates from rest to a speed of 20 m/s in 10 seconds, what is the average power output of the car's engine?
A.
2000 W
B.
4000 W
C.
6000 W
D.
8000 W
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Solution
First, calculate the work done: W = 0.5 * m * v^2 = 0.5 * 1000 kg * (20 m/s)^2 = 200000 J. Then, power is P = W/t = 200000 J / 10 s = 20000 W.
Correct Answer: C — 6000 W
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Q. If a 1000 W heater is used for 3 hours, how much energy does it consume in kilowatt-hours?
A.
3 kWh
B.
2 kWh
C.
1 kWh
D.
0.5 kWh
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Solution
Energy consumed in kilowatt-hours is calculated as E = P (kW) * t (h). Here, P = 1000 W = 1 kW and t = 3 hours. Thus, E = 1 kW * 3 h = 3 kWh.
Correct Answer: A — 3 kWh
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Q. If a 1000 W heater runs for 2 hours, how much energy does it consume?
A.
7200 J
B.
14400 J
C.
20000 J
D.
3600000 J
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Solution
Energy = Power × Time = 1000 W × (2 × 3600 s) = 7200000 J.
Correct Answer: D — 3600000 J
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Q. If a 2 kg object is dropped from a height of 5 m, what is its speed just before it hits the ground? (g = 10 m/s²)
A.
10 m/s
B.
5 m/s
C.
15 m/s
D.
20 m/s
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Solution
Using energy conservation: PE_initial = KE_final; m * g * h = 1/2 * m * v^2; v = sqrt(2gh) = sqrt(2 * 10 * 5) = 10 m/s
Correct Answer: A — 10 m/s
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Q. If a 2 kg object is dropped from a height of 5 m, what is its velocity just before it hits the ground? (g = 10 m/s²)
A.
10 m/s
B.
5 m/s
C.
15 m/s
D.
20 m/s
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Solution
Using energy conservation, v = sqrt(2gh) = sqrt(2 * 10 * 5) = 10 m/s
Correct Answer: A — 10 m/s
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Q. If a 3 kg object is moving with a speed of 4 m/s and comes to a stop, what is the work done by the friction force?
A.
-24 J
B.
-48 J
C.
-72 J
D.
-96 J
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Solution
Initial kinetic energy = 0.5 × 3 kg × (4 m/s)² = 24 J. Work done by friction = -24 J.
Correct Answer: B — -48 J
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Q. If a 3 kg object is moving with a speed of 4 m/s and comes to a stop, what is the work done by friction?
A.
-24 J
B.
-48 J
C.
0 J
D.
24 J
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Solution
Initial kinetic energy = 0.5 × m × v² = 0.5 × 3 kg × (4 m/s)² = 24 J. Work done by friction = -24 J.
Correct Answer: B — -48 J
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Q. If a 3 kg object is moving with a speed of 4 m/s and comes to a stop, what is the work done by the friction?
A.
-24 J
B.
-48 J
C.
-12 J
D.
-36 J
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Solution
Initial kinetic energy = 0.5 × 3 kg × (4 m/s)² = 24 J. Work done by friction = -24 J.
Correct Answer: B — -48 J
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Q. If a 3 kg object is moving with a speed of 4 m/s, what is the total mechanical energy if it is at a height of 2 m?
A.
30 J
B.
40 J
C.
50 J
D.
60 J
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Solution
Total mechanical energy = K.E + P.E = 0.5 × 3 kg × (4 m/s)² + 3 kg × 9.8 m/s² × 2 m = 24 J + 58.8 J = 82.8 J.
Correct Answer: C — 50 J
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Q. If a 3 kg object is moving with a velocity of 4 m/s, what is its momentum?
A.
12 kg m/s
B.
6 kg m/s
C.
8 kg m/s
D.
10 kg m/s
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Solution
Momentum (p) = m * v = 3 kg * 4 m/s = 12 kg m/s
Correct Answer: A — 12 kg m/s
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Q. If a 5 kg object is lifted to a height of 10 m, what is the potential energy gained by the object? (g = 9.8 m/s²)
A.
490 J
B.
980 J
C.
245 J
D.
2450 J
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Solution
Potential Energy = mass × g × height = 5 kg × 9.8 m/s² × 10 m = 490 J.
Correct Answer: B — 980 J
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Q. If a 5 kg object is lifted to a height of 10 m, what is the work done against gravity? (g = 9.8 m/s²)
A.
49 J
B.
98 J
C.
490 J
D.
980 J
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Solution
Work done = mgh = 5 kg × 9.8 m/s² × 10 m = 490 J.
Correct Answer: C — 490 J
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Q. If a 5 kg object is lifted to a height of 10 m, what is the work done against gravity?
A.
50 J
B.
100 J
C.
150 J
D.
200 J
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Solution
Work done = mgh = 5 kg × 9.8 m/s² × 10 m = 490 J.
Correct Answer: D — 200 J
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Q. If a car engine has a power output of 150 kW, how much work can it do in 2 minutes?
A.
18000 J
B.
9000 J
C.
30000 J
D.
180000 J
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Solution
Power is the rate of doing work. Work done can be calculated as W = P * t. Here, P = 150 kW = 150000 W and t = 2 minutes = 120 seconds. Thus, W = 150000 W * 120 s = 18000000 J.
Correct Answer: D — 180000 J
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Q. If a cyclist is moving at a constant speed and exerts a force of 200 N, what is the power output if the speed is 5 m/s?
A.
1000 W
B.
500 W
C.
200 W
D.
400 W
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Solution
Power can be calculated using P = F * v. Here, F = 200 N and v = 5 m/s. Thus, P = 200 N * 5 m/s = 1000 W.
Correct Answer: A — 1000 W
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Q. If a force of 10 N is applied to move an object 5 m in the direction of the force, what is the work done?
A.
50 J
B.
30 J
C.
20 J
D.
10 J
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Solution
Work Done (W) = Force * Distance = 10 N * 5 m = 50 J
Correct Answer: A — 50 J
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Q. If a force of 10 N is applied to move an object 5 m, what is the work done?
A.
50 J
B.
25 J
C.
10 J
D.
5 J
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Solution
Work Done (W) = Force * Distance = 10 N * 5 m = 50 J
Correct Answer: A — 50 J
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Q. If a force of 12 N is applied at an angle of 30 degrees to the horizontal while moving an object 3 m, what is the work done by the force?
A.
18 J
B.
24 J
C.
30 J
D.
36 J
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Solution
Work done = F × d × cos(θ) = 12 N × 3 m × cos(30°) = 12 N × 3 m × (√3/2) = 18 J.
Correct Answer: B — 24 J
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Q. If a force of 15 N acts on an object and moves it 4 m in the direction of the force, what is the work done?
A.
30 J
B.
60 J
C.
75 J
D.
90 J
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Solution
Work done = Force × Distance = 15 N × 4 m = 60 J.
Correct Answer: B — 60 J
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Q. If a force of 15 N is applied at an angle of 60 degrees to the horizontal while moving an object 4 m, what is the work done by the force?
A.
30 J
B.
60 J
C.
120 J
D.
180 J
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Solution
Work done = F × d × cos(θ) = 15 N × 4 m × cos(60°) = 15 N × 4 m × 0.5 = 30 J.
Correct Answer: C — 120 J
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Q. If a force of 15 N is applied at an angle of 60° to the horizontal while moving an object 4 m, what is the work done by the force?
A.
30 J
B.
60 J
C.
120 J
D.
180 J
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Solution
Work done = F × d × cos(θ) = 15 N × 4 m × cos(60°) = 15 N × 4 m × 0.5 = 30 J.
Correct Answer: C — 120 J
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Q. If a force of 15 N is applied to move an object 3 m in the direction of the force, what is the work done?
A.
45 J
B.
30 J
C.
15 J
D.
60 J
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Solution
Work done = Force × Distance = 15 N × 3 m = 45 J.
Correct Answer: A — 45 J
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Q. If a force of 15 N is applied to move an object 4 m in the direction of the force, what is the work done?
A.
30 J
B.
60 J
C.
45 J
D.
75 J
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Solution
Work done = Force × Distance = 15 N × 4 m = 60 J.
Correct Answer: B — 60 J
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Q. If a force of 5 N acts on an object and moves it 4 m in the direction of the force, what is the work done?
A.
10 J
B.
15 J
C.
20 J
D.
25 J
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Solution
Work done = Force × Distance = 5 N × 4 m = 20 J.
Correct Answer: C — 20 J
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Q. If a force of 5 N is applied at an angle of 60 degrees to the horizontal while moving an object 4 m, what is the work done by the force?
A.
10 J
B.
20 J
C.
5 J
D.
15 J
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Solution
Work done = Force × Distance × cos(θ) = 5 N × 4 m × cos(60°) = 5 N × 4 m × 0.5 = 10 J.
Correct Answer: A — 10 J
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Q. If a force of 5 N is applied at an angle of 60 degrees to the horizontal while moving an object 3 m, what is the work done by the force?
A.
7.5 J
B.
15 J
C.
12.99 J
D.
10 J
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Solution
Work done = Force × Distance × cos(θ) = 5 N × 3 m × cos(60°) = 5 N × 3 m × 0.5 = 7.5 J.
Correct Answer: C — 12.99 J
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Q. If a machine does 200 J of work in 5 seconds, what is its power output?
A.
20 W
B.
40 W
C.
50 W
D.
60 W
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Solution
Power = Work / Time = 200 J / 5 s = 40 W.
Correct Answer: B — 40 W
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Q. If a machine does 2000 J of work in 5 seconds, what is its power output?
A.
200 W
B.
400 W
C.
500 W
D.
600 W
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Solution
Power = Work / Time = 2000 J / 5 s = 400 W.
Correct Answer: B — 400 W
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Q. If a machine does 500 J of work in 10 seconds, what is its power output?
A.
50 W
B.
100 W
C.
200 W
D.
500 W
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Solution
Power is calculated using the formula P = W/t. Here, W = 500 J and t = 10 s. Thus, P = 500 J / 10 s = 50 W.
Correct Answer: B — 100 W
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