Unit Eight: Power

Today in physics we talked about power. Power is the rate at which work is being done. So power = work/interval of time = Joules/seconds = watt. We also worked on how to use the equations from last class which are:

W = Fd

PEg = mgh

PEs = ½kd²

Fs = -kd

KE = ½mv²
∆E = W = f×d = mg×h

W = work

F = force

d = distance

m = mass

g = gravity = 9.8 m/s² ≈ 10m/s²

v = velocity
h = height
∆E = total energy

PEg = Potential Energy (gravitational)
PEs = Potential Energy (of spring)
Fs = Force of spring
KE = kinetic energy

With the given variables you could calculate a machine's (because objects don't move on their own) potential or kinetic energy. Like for example, (just so you know these numbers I am about to use may not logically make sense so just go with it) a machine with a mass of 60 kg walks up one flight of stairs with a distance of 4 m.

1. Calculate the work done by the machine.
2. Find the velocity.

To find #1:
Using the equation we learned from earlier units, F = ma, it should look like this: F = 60kg×9.8m/s². F = 588 N. Now that you know the force, you can use the equation W = F×d, it should look like this: W = 588N×4m. W = 2.352×10³ J.

To find #2:
Using the equations KE = ½mv² and PEg = mgh, input the givens into the equations so it looks like this:

½(60kg)(v)² = 60kg(9.8m/s²)(4m)

Now calculate:

½(60kg)(v)² = 2.352×10³ J

60kg(v)² = 4.704×10³ J

v² = 78.4 N m²/s²

v ≈ 8.9 m/s

Here is the machine/robot going up the flight of stairs.