1. Chapter 5 Review

2. Work is force x distance
Only the force parallel to the
displacement applies to the work

3. Calculate the work done by the pull
Fpull = 20N
Pulling a box
N = 137.2N
f = -16.5N
Fpull = 20N
Fpully = sin30°
20N = 10N
30°
angle = 30°
Fpullx = cos30°(20N) = 17.3N
mass = 15 kg
mg = N
Label and calculate all forces
pulled 8 m
m = .12
Calculate the work done by the pull
and friction
Wpull = Fxd = 138.4J
Wf = fd = -132J

4. Potential Energy is energy of position
GPE = mgh
affected by height
EPE = ½kx2
affected by distance squeezed or pulled
k is the spring constant

5. if I triple the speed of something
Kinetic Energy is energy of motion
KE = ½mv2
affected by velocity
if I triple the speed of something
what happens to it’s KE?

6. Mechanical Energy is PE + KE
MEi = MEf
if there is no friction
if there is friction, some KE
is changed to heat and lost

7. raise the ball of a pendulum
40 J of work is done to
raise the ball of a pendulum
parallel to the ground
30° ½h
If it is released how much KE,
PE and ME will it have after 30°? ½h
At its lowest point, how much KE,
PE and ME does it have?

8. What will the wagon’s speed be at the bottom of the hill?
3 m/s
What will the wagon’s speed
be at the bottom of the hill?
KEi + PEi = KEf
½mv2i + mghi = ½mv2f
10 m
v2f = v2i + 2ghi
vf = 14.3 m/s

9. against a spring with a spring constant of 240 N/m
A 5 kg block is pushed 20 cm
against a spring with a spring
constant of 240 N/m
5 kg
What is the stored elastic potential energy?
EPE = ½kx2
= ½(240N/m)(.2 m)2
= 4.8 J
If released, what is the velocity of the block, as it comes
off the spring?
KE = EPE = 4.8 J = ½mv2
v = 1.39 m/s
If 4 N of frictional force is acting between the floor and
block, what distance will the block go?
W = DKE
= f d
d = DKE / f
= 4.8 J / 4 N
= 1.2 m