- Get a copy of the Power Guided notes and fill them in as you read through this passage.
- The last section we talked about work. Now we are looking at Power and Power is the rate at which work is done.
- Power equals the amount of work done divided by the time interval during which the work is done.
- The equation for calculating Power is power equals work divided by time.
- If you have twice the amount of power, twice the amount of work is done. So power and work are directly proportional. Basically if you increase on you will increase the other.
- If you have an engine with twice the amount of power it will take half the time to reach a given speed. So power and time are inversely proportional. Basically as one increases the other is decreasing.
- The units for work if you remember is Joules (J) and the units for time is seconds (s). The unit for power is Watts and is written as a capital W.
- 1 Watt of power is expended when 1 Joule of work is done in 1 second.
- If you remember when we talked about work we discussed that there are two different types of work, one that is working against a force and one that is changing speed. Some examples of work being done would include lifting a barbell in 5 seconds and a car accelerating over 10 seconds. Pushing against a wall for 10 seconds would not be an example of power because if you remember if there is not distance moved there is no work. If there is no work then there is no power.
- Now for the practice problems. make sure to use the equation and show your work. Number one you are given distance = 0.05 m, work = 0.50 J, and time = 2 s. Remember your equation is power equals work divided by time. Since you are given work and time the distance does not matter so you will take 0.50 J divided by 2 s to get P = 0.25 W.
- Number two is more difficult. You are given mass = 42.0 kg, distance = 0.25 m, and time = 2 s. Remember your power equation is work divided by time. While you have been given time you do not yet know the work that has been done so lets go back to that. To calculate work that is done you need the force and multiply is by the distance. You know the distance but you do not know the force. if you remember weight is a measure of force and can be found by multiplying the mass of an object by gravity which on Earth is 9.8 m/s2. So in order to find weight you can take your mass of 42 kg and multiple it by gravity of 9.8 m/s2 to find the force is equal to 411.6 N. Now that you have your force you can find your work by multiplying your force of 411.6 N by your distance of 0.25 m to find the work is equal to 102.9 J. Now that you have your work you can find your power by taking your work of 102.9 J and dividing it by your time of 2 s to find your power is equal to 51.45 W.
- Now that you have your notes filled in you need to complete the power problem ws.
- Once everyone is done you will be going over the sheet on the white board. Individuals will be chosen for certain problems and you should show all work.