WORK AND POWER

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Transcript WORK AND POWER

WORK AND POWER
Work- when a force is applied over a
distance in the direction of the motion.
Scalar quantity
Work = Force x distance
W = Fd
Unit: Nm or Joule (J)
Ex 1: A 40kg cart is rolled along the floor by a
horizontal force at a constant velocity. If 150N
is applied to the cart for 10m, how much work
is done?
F = 150N
W = Fd
W = 150N( 10m)
W= 1500J
Ex 2: A sailor pulls a boat along a dock for 30m
with a force of 250N. What work is done if the
rope is held at 60° with respect to the water?
Fp = F cos—≤
Fp = 250N cos 60°
Fp = 125N
60°
Fp
W = Fp d
W= 125N(30m)
W= 3750 J
SIMPLE MACHINES
a) Redirects the applied force
b) Breaks job up into smaller repetitions
Levers
Pulleys
Gears
wedge
wheel and axel
Work output - Work done by a machine.
Work input -work done to operate the machine.
%Efficiency = Work output x 100
Work input
Ex: A pulley system lifts a 90N crate 3m up. If a man applies
30N of force for a length of 15m, what is the efficiency of the
pulley system?
%E = (90N)(3m) x100 = 60% efficient
(30N)(15m)
Where did the other 40% go?
POWER- The rate of doing work
Power = Work
time
P= W/t = (Fd)/t = Fv
Unit: J/s or watt (W)
*English unit= horse power (746 watts)*
Ex: A machine produces a force of 40N over a
distance of 100m. If it does this in 5.0
seconds, what is the power of the machine in
watts and kilowatts?
P = Fd/t
P = 40N( 100m)
5.0 sec
P= 800 W
P = 0.80 kW