Transcript Slide 1

Chapter 3.3-3.4
Review
1. Two forces are applied
to a stump by two tractors.
One is a 150 N force to
the east. The other is
100 N in a direction 35°
north of east. What is the
resultant force?
sin35° = Fnorth /100
Fnorth = 57 Nnorth
cos35° = Feast /100
Feast = 82 Neast
150 Neast + 82 Neast =
232 Neast
2
232
2
57
+
=
c = 238 N
tanq = 57/238
2
c
13.5° north of east
2. A jogger runs
1200 m in a direction
65° south of west. He
then runs 1300 m west.
What is his total
displacement?
sin65° = S /1200
S = 1088 msouth
cos65° = W/1200
W = 507 mwest
1300 mwest + 507 mwest
= 1807 mwest
2
1807
2
1088
+
=
c = 2109 m
tanq = 1088/1807
31° south of west
2
c
3. An Aggie pushes his car with
a force of 500 N. Because he
forgot to release the parking
brake, the ground pushes on the
car with a force of 500 N in the
opposite direction. What is the
net force on the car?
0, the net force is
500 N + (–500 N) =
0N
4. What are the
components of
projectile motion? What
shape does the path of
an object in projectile
motion take?
The components of
projectile motion are initial
horizontal velocity, object
only under the force of
gravity, and no air
resistance. The shape of
the path is a parabola.
5. Why don’t
projectiles on
earth really follow
the path of a
parabola?
Air resistance
slows the object.
6. Which of these objects are in projectile
motion?
A. a rocket being launched
B. a thrown baseball
C. a cat jumping down from the roof
D. a wheel falling from the landing gear of an
airplane
E. a pecan nut falling off the limb of a pecan
tree
F. a leaf falling from a tree
G. a rock sinking through the water in a pond
H. a flying paper airplane
6. Which of these objects are in projectile
motion?
B. a thrown baseball
C. a cat jumping down from the roof
D. a wheel falling from the landing gear of an
airplane
E. a pecan nut falling off the limb of a pecan
tree
(All the others have some
other force on them.)
7. Which of the
choices above
move with a
parabolic motion?
7. Which of the choices above move with a
parabolic motion?
B. a thrown baseball
C. a cat jumping down from the roof
D. a wheel falling from the landing gear of an
airplane
(If it is in projectile motion it follows
a parabola, except for the pecan
nut which has no horizontal
velocity.)
8. A bag of flour falls from
an airplane flying level at
150 m/s at a height above
the ground of 290 m. How
long does it take the bag
to fall to the ground?
y = v0 t + ½
290 = ½
2
10(t)
t = 7.6 s
2
gt
9. With what vertical
velocity does the bag
in question 8 hit the
ground?
v = v0 + gt
v = 0 + 10(7.6)
v = 76 m/s
10. With what
horizontal velocity
does the bag in
question 8 hit the
ground?
150 m/s
The horizontal
velocity doesn’t
change as it falls.
11. With what velocity
does the bag in
question 8 hit the
ground? Don’t forget
direction!
2
150
2
76
2
c
+
=
c = 168 m/s
tanq = 76/150
27°
below horizontal
12. How far does the
bag in question 8
travel horizontally
before it hits the
ground?
150 m/s x 7.6 s =
1140 m
13. A bullet is fired at a
velocity of 1000 m/s at an
angle of 22° to the ground.
What is the vertical
component of the bullet’s
velocity?
sin22° = vv /1000
vv = 375 m/s
14. How long is the
bullet in question
13 in the air?
v = v0 + gt
0 = 375 + (-10)t
t = 37.5 s
37.5 s x 2 = 75 s
15. What is the
horizontal velocity
of the bullet in
question 13?
cos22° = vh /1000
vh = 927 m/s
16. How far does
the bullet in
question 13 travel
before hitting the
ground?
927 m/s x 75 s =
69525 m
17. An athlete in the shot put
competition launches a shot at an
angle of 50° to the ground. The
initial velocity of the shot is 14 m/s.
What distance does the shot travel
before hitting the ground?
sin50° = vv /14
vv = 10.7 m/s
v = v0 + gt
0 = 10.7 + (-10)t
t = 1.07 s
1.07 s x 2 = 2.14 s
cos50° = vh /14
vh = 9 m/s
9 m/s x 2.14 s =
19.26 m
18. You are riding in a car
moving 35 m/s to the east.
You are tossing a ball straight
up and catching it as it falls.
Describe the velocity of the
ball from your perspective.
The ball appears to
move straight up and
straight down.
19. Describe the velocity
of the ball in question 18
as viewed by a pedestrian
standing at the side of the
road as your car passes.
It appears to
follow a parabola
on each toss.
20. A car slowly rolls off a cliff
and falls 230 meters to the
river below. How long does it
take the car to fall to the
water? How long does it take
the car to fall if it has an initial
horizontal velocity of 40 m/s?
y = v0 t + ½
230 = ½
2
10(t)
t = 6.8 s
2
gt
t = 6.8 s
Horizontal
velocity doesn’t
affect the vertical
motion.