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# Work > Power

Thackyt
Have you ever had trouble in Physics?

Well contact me for more help.

This topic will cover Work, Power, and Efficiency.

Work = Force * distance
Power = Work / Time

Force or Weight = Mass * Gravity

Gravity = -9.8 meters/second^2 (on Earth)

E1. After scoring a touchdown, an 83.0 kilogram wide receiver celebrates by leaving 129 centimeters off the ground. How much work did he do during his celebration?

Work = Force * distance

We are not given force. Force or Weight = Mass * Gravity

Force = 83.0 kilogram * -9.8 meters/second^2
Force = -813.4 N
Work = -813.4 N * distance

Work requires distance to be in meters.

There are 100 centimeters in 1 meter so.

129 centimeters / 100 = 1.29 meters

Work = -813.4 Neutons * 1.29 meters

Work = 1049.286 Neuton * meters or Joules

But we are not done yet. REMEMBER SIGNIFICANT DIGITS!

We are given 83.0 m and 129 cm so then we look at which has the least Significant Digits

83.0 m has the least, it has three so we must use two significant digits, and round our work.

so work is actually equal to 1050 Joules

Now lets say that 1050 Joules is applied for 31.32 Seconds. How much power does this emit?

Power = Work / Time
Work = 1049.286 Joules (always use unrounded)
Time = 31.32 Seconds

Power = 1049.286 Joules / 31.39 Seconds
Power = 33.42739726 Joules / Seconds or Watts (REMEMBER SIGNIFICANT DIGITS)
Power = 33.43 Watts

Bikerman
Your expression of force is limited (and therefore not correct).
f=ma
In specific calculations one may be interested in the 'force' of gravity - as in your example here, in which case you can write f=mg, but in many calculations there are other forces which one needs to factor, and force in such cases cannot be written f=mg.

Additionally, the unit of force is the Newton, not the neuton.
_AVG_
I don't know whether you were talking about the power supplied when 1050 J of work is done every second in relation to the example you earlier described. If you were, then your analysis of power is not correct since the player does not do 1050 J of work every second. He distributes this over the total time he takes to jump up to 1.29m. The relevant power can probably be calculated in the following way:

Power = Force*average velocity

This is just the average power since the velocity is not a constant instantaneously.
chatrack
Hi,

In equation for efficiency ,

efficiency = output power/input power

Here output Power = 33.43 Watts , since output took place in a time 31.32 Seconds to make a jump to a height of 1.29m

To find the input power, we need the time taken to Do the work done.
asnani04
Power and work are really useful concepts. They ar used to solve many questions directly without the burden of solving multiple equations on force and torque. Conservation of energy is a great technique in physics.
nguyenvulong
in my opinion, works bring passion and vice versa
and passion surely bring you power