mg sin20° acts down the slope mg cos20° acts into the slope. Note that the gravitational force is the only force which needs to be split into components. If the total resistance forces acting on the car add to 500 N, what is the power output of the car in watts? In horsepower? This works out to 40 N.Ī car with a mass of 900 kg climbs a 20° incline at a steady speed of 60 km/hr. Assuming there aren't any other forces acting against you, then dividing this by your speed should give you the force the air exerts on you. The power used to overcome air resistance is 80% of 500 W, which is 400 W. If you assume that 80% of this energy is going to overcome air resistance, how much force is the air exerting on you? You're riding into a headwind, and you're burning up energy at the rate of 500 J/s. Let's say you're riding your bicycle on a level road at a constant speed of 10 m/s. Here's an example of when you might use this. Power : P = F v (F is the force in the direction of the velocity) Power : P = F s / t (F is the force in the direction of s, the displacement)ĭisplacement over time is velocity, so power can also be written in this form: Power is work over time, and work is force multiplied by distance. In other words, on the average, we're just a little brighter than your average light bulb. Figuring out our average power output, we simply divide the energy by the number of seconds in a day, 86400, which gives a bit more than 100 W. Most of us take in something like 2500 "calories" in a day, although what we call calories is really a kilocalorie assuming we use up all this energy in a day (a reasonable assumption considering we'll have to eat tomorrow, too) we can use this as our energy output per day.įirst, take the 2.5 x 10 6 cal and convert to Joules, using the conversion factor 4.18 J / cal.
This can be determined from the amount of energy we consume in a day in the way of food. The unit for power is the watt (W).Īn interesting calculation is the average power output of a human being. Power is the rate at which work is done and the rate at which energy is used. Computers have more calculating power than we do a sports car generally has a more powerful engine than an economy car. Power is the measure of how fast work is done.
Being able to do work is not just what's important how fast you can do work is also an important factor.