Transcript 5.3 Worksheet

Chapter 5.3
Review
1. What has a greater
effect on kinetic
energy, changing
mass or changing
velocity? Why?
Changing
velocity, because
it is squared in
the equation.
2
KE = ½ mv
2. List the types
of energy that
make up
mechanical
energy.
Gravitational
potential energy,
elastic potential
energy,
and kinetic energy.
3. What does it
mean when we
say mechanical
energy is
conserved?
The total amount of
mechanical energy remains
the same. It can change
from one type of mechanical
energy to another, but the
total amount remains the
same.
4. A spring of spring constant
100 N/m is compressed
0.1 m. A ball of mass
0.030 kg is placed on top
of the spring, and the
spring is released.
What is the maximum height
the ball reaches?
PEg = PEe
2
mgh = ½ kx
(.03)10h =
2
½(100)0.1
h = 1.67 m
5. When the ball in
question 4 falls back
to earth, what is its
velocity when it hits
the ground?
PE = KE
2
mgh = ½ mv
(0.03)10(1.67) = ½
2
0.03v
v = 5.8 m/s
6. A car on a roller
coaster tops a hill at a
speed of 5 m/s. The hill is
100 m in height. What is
the speed of the car at
the bottom of the hill?
PE + KE0 = KEf
mgh + ½
2
mv0
=½
2
2
mvf
gh + ½v0 =
2
½vf
10(100) +
=
2
½(5)
vf = 45 m/s
2
½vf
7. I pick up 20 books, one at a
time, and set them on a table.
You pick up all 20 books at once
and set them on the table.
Which one of us did the most
work? Which one of us
expended the most power?
The amount of work
was the same.
You expended more
power because the
work was done
faster.
8. What does the
power rating of a
machine indicate
about its rate of
energy production?
The power rating
IS the rate
of energy
production!
9. What are the
two formulas for
calculating
power?
P = W/t
P = Fv
10. A 60 kg firefighter
climbs a 20 m ladder in
40 seconds. How much
work did the firefighter do?
How much power was
expended by the
firefighter?
W = Fd
W = mgh
W = 60(10)20
W = 12000 J
P = W/t
P = 12000/40
P = 300 watts
11. A 500 kg motorcycle
accelerates from rest to
a speed of 25 m/s in
15 seconds. What is the
average power produced
by the engine of the
motorcycle?
F = ma
F = 500(25/15) = 833 N
2
d = ½ at
d = ½ (25/15)(15)2 = 187.5
P = Fd/t
P = 833(187.5)/15
P = 10400 W
OR
P = Fv
The force is still 833 N, v is
the average velocity 25/2 =
12.5 m/s.
P = 833 x 12.5 m/s
P = 10400 W