The action where by the force acts on
an object through a displacement to
transfer energy from one place or form
to another.
W-Work
Unit: Joules (J)
F- force
D-displacement
theta- angle between
the displacement and
the force vectors
Stored energy of position possessed
by an object.
Units: Joules (J)
There are two types of potential
energy:
Spring & Gravitational
Gravitational
PEgrav = mass * g * height
PEgrav = m * g * h
g- acceleration due
to gravity--- 9.8 m/s
Spring
The energy stored in elastic materials as the result of their stretching
or compressing
The energy of motion
where m = mass of object
v = speed of object
Unit: Joules (J)
The energy which is possessed by an object
due to its motion or due to its position
TME = PE + KE
TME = PEgrav + PEspring + KE
The rate at which work is done
Unit: Watt (W)
Practice
1. Two physics students, Will N. Andable and Ben
Pumpiniron, are in the weightlifting room. Will lifts
the 100-pound barbell over his head 10 times in one
minute; Ben lifts the 100-pound barbell over his
head 10 times in 10 seconds. Which student does the
most work? ______________ Which student delivers
the most power? ______________ Explain your
answers.
Ben and Will do the same amount of work. They
apply the same force to lift the same barbell the
same distance above their heads.
Yet, Ben is the most "power-full" since he does the
same work in less time. Power and time are
inversely proportional.
When doing a chin-up, a physics student
lifts her 42.0-kg body a distance of 0.25
meters in 2 seconds. What is the power
delivered by the student's biceps?
W = F * d = (411.6 N) * (0.250 m) W = 102.9 J
The power is the work/time ratio which is (102.9 J) / (2 seconds) = 51.5 Watts
Calculate the work done by a 2.0-N
force (directed at a 30° angle to the
vertical) to move a 500 gram box a
horizontal distance of 400 cm across a
rough floor at a constant speed of 0.5
m/s. (HINT: Be cautious with the
units.)
W = (2.0 N) * (4.00 m) * cos (60 degrees) =
4.0 J
1. A cart is loaded with a brick and pulled at
constant speed along an inclined plane to the height of a seat-top. If
the mass of the loaded cart is 3.0 kg and the height of the seat top is
0.45 meters, then what is the potential energy of the loaded cart at
the height of the seat-top?
PE = m*g*h
PE = (3 kg ) * (9.8 m/s/s) * (0.45 m)
PE = 13.2 J
PEgrav = mass * g * height
PEgrav = m * g * h
2
TME = PE + KE