You’re applying constant force. The force is causing the object to move in the direction of the force.
Whenever you read a word problem about work, stop and think where the force is being applied. If you lift a box, you’re pushing upward, and the box is moving up — so the distance is however much it rises. But if you then walk forward holding the box, there’s no work happening at all. You’re pushing upward still, to keep the box from falling, but the box isn’t moving up. [3] X Research source
Avoid using pounds or other non-standard units, or your final answer won’t be in terms of joules.
If the object is being moved horizontally, gravity is irrelevant. The problem may ask you to calculate the force required to overcome friction instead. If the problem tells you how fast the object is accelerating when it is pushed, you can multiply the acceleration given with the mass.
If the problem gives you the “rightward force,” “upward force,” or “force in the direction of motion,” it has already calculated the “force x cos(θ)” part of the problem, and you can skip down to multiplying the values together
In our example, the angle θ between the flat snow and the rope is 30º. Calculate cos(θ). cos(30º) = (√3)/2 = about 0. 866. You can use a calculator to find this value, but make sure your calculator is set to the same unit as your angle measurement (degrees or radians). Multiply the total force x cos(θ). In our example, 10N x 0. 866 = 8. 66 N of force in the direction of motion.
This formula works for any form of power measured in watts, but electricity is the most common application.
Kinetic energy is equivalent to the amount of work done to accelerate a stationary object to a certain speed. Once it has reached that speed, the object retains that amount of kinetic energy until that energy transforms into heat (from friction), gravitational potential energy (from moving against gravity), or other types of energy.
If the bicyclist moved at a constant rate (didn’t accelerate), measure the distance the bicyclist traveled in meters, and divide it by the number of seconds it took to move that distance. This will give you the average speed, which in this scenario is the same as the speed at any given moment. If the bicyclist is accelerating at constant acceleration and doesn’t change direction, calculate his speed at time t with the formula “speed at time t = (acceleration)(t) + initial speed. Use seconds to measure time, meters/second to measure speed, and m/s2 to measure acceleration.
The kinetic energy formula can be derived from the definition of work, W = FΔs, and the kinematic equation v2 = v02 + 2aΔs. [12] X Research source Δs refers to “change in position,” or the amount of distance traveled.
Use grams, not any other unit, or the result will not be in Joules.
Specific heat capacity actually varies slightly based on temperature and pressure. Different organizations and textbooks use different “standard temperatures,” so you may see the specific heat capacity of water listed as 4. 179 instead. You can use Kelvin instead of Celsius, since a difference in temperature is the same in both units (heating something by 3ºC is the same as heating by 3 Kelvin). Do not use Fahrenheit, or your result will not be in Joules.
If you want to measure the total amount of energy stored as heat, you can pretend the initial temperature was absolute zero: 0 Kelvin or -273. 15ºC. This is not typically useful.
Heat is more commonly expressed in the metric system in terms of either calories or kilocalories. A calorie is defined as the amount of heat required to raise the temperature of 1 gram of water 1 degree Celsius, while a Kilocalorie (or Calorie) is the amount of heat required to raise the temperature of 1 kilogram of water 1 degree Celsius. In the example above, raising 500 grams of water 20 degrees Celsius would expend 10,000 calories or 10 kilocalories.
As joules are small units, and because appliances commonly use watts, milliwatts, and kilowatts to indicate how much power they use, utilities commonly measure their energy output in kilowatt-hours. One watt equals 1 joule per second, or 1 joule equals 1 watt-second; a kilowatt equals 1 kilojoules per second and a kilojoule equals 1 kilowatt-second. As there are 3,600 seconds in an hour, 1 kilowatt-hour equals 3,600 kilowatt-seconds, 3,600 kilojoules, or 3,600,000 joules.
