# what does comparing the stated value of 112 hp mean?

so for my physics homework we have to make an analysis of data about pushing a car. i have all the data and answered all the questions (find the work done, find the power, find the velocity, the acceleration etc). But after finding the horse power (assuming 1 horsepower=745 watts, according to the internet not the teacher), there is a question that says "Calculate the power in horse power, compare this with the stated value of 112 hp."

what does this mean? i cannot contact the teacher for reasons i cant share

Relevance

The value of 112 hp is the power output of the car's engine shown ['stated'] in the specification sheet for that model of car.

You are asked to work out the power output you managed to produce by pushing the car, convert that value into horsepower and then compare that to the power produced by the car's engine.

So if you managed to produce say, 0.7 hp, you would say that this represented

0.7 / 112 = 0.006 of the engine's rated power.

Alternatively, you could give it as a percentage (0.7 * 100) / 112 = 0.6%

[Incidentally 1 hp is a bit nearer to 746W than 745]

• Car manufacturers rate the horsepower of their engines under ideal conditions ( temperature pressure engine in perfect tune air with nopollutents etc) The actual horsepower actually available is usually less.

They rate the "shaft horsepower " at the crankshaft. Accounting for losses through the drivetrain the wheels. Thus your calculated horsepower will require a larger engine to get that power at the wheels

The torque curve could result in the rated horsepower being generated at an impractical RPM. (400 HP @ 1500 RPM is not very useful for a car)

How does your calculated power requirement match the stated power from the manufacturer?

• according to the google: "1 watt = 0.00134102209 horsepower" or as you said "1 horsepower = 745.7 W"

so take your calculated value of the power in Watts and divide it by 745.7 -> that'll be the power in horsepower that you're supposed to compare to a value of 112 horsepower