Work, Energy and Power. Work. W = Fs W= work F = force s = displacement Whe a force makes an object move, work has been done. Whenever work is done, energy is transferred form one place to another or transformed from one form to another. Units are = 1Nm = 1J(joule). Practice Problem 1.
W = Fs
Work isn’t always done in a stratight line. That means we have to take into account the direction of the displacement. This is done by adding “cosθ” to the equation.
There are lots of different forms of energy.
speed and mass
result of its position
At a railway station, two trains slowly collide in order to “couple” (join together). If one train of mass 12000kg is moving at 0.75m/s and the other of mass 3000kg is stationary, calculate the velocity of the two as they move away.
We already solved this for .6m/s. Now tell me the kinetic energies before and after the collision.
PART A: His feet will stop when they hit the ground but his body will still be travelling forward at the bike speed, so he will fall over forwards.
PART B: 4m/s
PART C: before – 250J
after – 400J
The increase in KE is due to energy provided or work done by the boy pushing on the bicycle.
Remember: P = W/t
Quick review: what is work?
Quick review: what is velocity?
The SI unit of power is the watt.
Horsepower is also a unit.