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Horsepower worksheet

Grades 8–9 · CCSS HSN.Q.A.1

Solve each problem and show your work. Round answers to 2 decimal places where needed.

1.
Problem 1.
- Work out horsepower from: Weight and quarter-mile time
- Race weight (car plus driver): 2,500 lb
- Quarter-mile elapsed time (ET): 12 s
Find: Estimated horsepower
Answer
2.
Problem 2.
- Work out horsepower from: Weight and trap speed
- Race weight (car plus driver): 4,000 lb
- Trap speed at the end of the quarter mile: 100 mph
Find: Estimated horsepower
Answer
3.
Problem 3.
- Work out horsepower from: Weight and quarter-mile time
- Race weight (car plus driver): 3,800 lb
- Quarter-mile elapsed time (ET): 11.5 s
Find: Estimated horsepower
Answer
4.
Problem 4.
- Work out horsepower from: Weight and trap speed
- Race weight (car plus driver): 3,200 lb
- Trap speed at the end of the quarter mile: 110 mph
Find: Estimated horsepower
Answer
5.
Problem 5.
- Work out horsepower from: Torque and RPM
- Torque: 250 lb·ft
- Engine speed: 3,000 rpm
Find: Horsepower
Answer
6.
Problem 6.
- Work out horsepower from: Torque and RPM
- Torque: 300 lb·ft
- Engine speed: 2,000 rpm
Find: Horsepower
Answer
7.
Problem 7.
- Work out horsepower from: Torque and RPM
- Torque: 150 lb·ft
- Engine speed: 4,000 rpm
Find: Horsepower
Answer
8.
Problem 8.
- Work out horsepower from: Torque and RPM
- Torque: 350 lb·ft
- Engine speed: 5,000 rpm
Find: Horsepower
Answer
9.
Problem 9.
- Work out horsepower from: Weight and trap speed
- Race weight (car plus driver): 3,000 lb
- Trap speed at the end of the quarter mile: 120 mph
Find: Estimated horsepower
Answer
10.
Problem 10.
- Work out horsepower from: Weight and quarter-mile time
- Race weight (car plus driver): 3,800 lb
- Quarter-mile elapsed time (ET): 14 s
Find: Estimated horsepower
Answer

Answer key: Horsepower worksheet

1. Estimated horsepower: 285.9 hp
1. Use the time rule of thumb. Divide 5.825 by the time. Cube it, which means times itself three times. Then times the weight
  $2,500 lb \times {(\frac{5.825}{12 s})}^{3}$ $= 285.9 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $285.9 hp \times 0.7456999$ $= 213.23 kW$
2. Estimated horsepower: 312.2 hp
1. Use the speed rule of thumb. Divide the speed by 234. Cube it, then times the weight
  $4,000 lb \times {(\frac{100 mph}{234})}^{3}$ $= 312.2 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $312.2 hp \times 0.7456999$ $= 232.8 kW$
3. Estimated horsepower: 493.8 hp
1. Use the time rule of thumb. Divide 5.825 by the time. Cube it, which means times itself three times. Then times the weight
  $3,800 lb \times {(\frac{5.825}{11.5 s})}^{3}$ $= 493.8 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $493.8 hp \times 0.7456999$ $= 368.25 kW$
4. Estimated horsepower: 332.4 hp
1. Use the speed rule of thumb. Divide the speed by 234. Cube it, then times the weight
  $3,200 lb \times {(\frac{110 mph}{234})}^{3}$ $= 332.4 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $332.4 hp \times 0.7456999$ $= 247.88 kW$
5. Horsepower: 142.8 hp
1. Multiply torque by rpm. Then divide by 5,252.1, which is 33,000 ÷ 2π. That gives horsepower
  $\frac{250 lb·ft \times 3,000 rpm}{5,252.113}$ $= 142.8 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $142.8 hp \times 0.7456999$ $= 106.49 kW$
6. Horsepower: 114.2 hp
1. Multiply torque by rpm. Then divide by 5,252.1, which is 33,000 ÷ 2π. That gives horsepower
  $\frac{300 lb·ft \times 2,000 rpm}{5,252.113}$ $= 114.2 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $114.2 hp \times 0.7456999$ $= 85.19 kW$
7. Horsepower: 114.2 hp
1. Multiply torque by rpm. Then divide by 5,252.1, which is 33,000 ÷ 2π. That gives horsepower
  $\frac{150 lb·ft \times 4,000 rpm}{5,252.113}$ $= 114.2 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $114.2 hp \times 0.7456999$ $= 85.19 kW$
8. Horsepower: 333.2 hp
1. Multiply torque by rpm. Then divide by 5,252.1, which is 33,000 ÷ 2π. That gives horsepower
  $\frac{350 lb·ft \times 5,000 rpm}{5,252.113}$ $= 333.2 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $333.2 hp \times 0.7456999$ $= 248.47 kW$
9. Estimated horsepower: 404.6 hp
1. Use the speed rule of thumb. Divide the speed by 234. Cube it, then times the weight
  $3,000 lb \times {(\frac{120 mph}{234})}^{3}$ $= 404.6 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $404.6 hp \times 0.7456999$ $= 301.7 kW$
10. Estimated horsepower: 273.7 hp
1. Use the time rule of thumb. Divide 5.825 by the time. Cube it, which means times itself three times. Then times the weight
  $3,800 lb \times {(\frac{5.825}{14 s})}^{3}$ $= 273.7 hp$
2. Change horsepower to kW. One horsepower is about 0.7457 kW
  $273.7 hp \times 0.7456999$ $= 204.1 kW$