Name: _______________________________________________________ Date: _________________ Per:__________
Week 12 DCA
(Projectile Motion, Circular Motion, Universal Gravitation)
Forces Portion:
1. List and example of Newton’s first, second and third law.
1st Law -
2nd Law -
3rd Law –
2.
Newton’s 2nd Law says that force and acceleration are
A.
directly related
B. inversely related. C. not related.
3. True or False: An object experiencing a net force of zero must be stationary. Explain your
answer.
4.
A crate has a mass of 45 kg. What is the weight of the crate? Fw = mg
5.
A crate has a weight of 56 N. What is the mass of the crate?
Fw = mg
6. An object is acted on with 45N of force to the left and 30N of force to the right. Draw a free
body diagram and give the net force on the object.
7. A clothesline holds 50N of laundry. The laundry is suspended in the center of the line with
both ropes at equal angels. What is the tension in each line?
8.
What is less, your weight on the Earth or your weight on the moon?
9.
What is less, your mass on the Earth or your mass on the moon?
10. The Normal force is usually the same size as the _______________ force. (or weight)
11. A horizontal force of 45N gives a 6.2kg block an acceleration of what magnitude?
12. Below, the net force is shown for each situation. Analyze each situation and determine the
magnitude of the unknown forces.
A.______ B._______
C._____
D._____ E._____
13. A hockey player accelerates a puck (m = 0.167 kg) from rest to a velocity of 50 m/s in
0.0121 sec. Determine the acceleration of the puck and the force applied by the hockey stick
to the puck. Neglect resistance forces.
Circular Motion
14. Which has greater linear speed, a horse near the outside rail of a merry-go-round or a horse
near the inside rail? (Hint: Think radius)
15. Why does a tin can whirled on the end of a string move in a circle?
16. If you whirl a tin can on the end of a string and the string suddenly breaks, the can will go in
what direction?
17. List the units for the following:
Tangential Speed ____________
Period _____________
Centripetal Acceleration ________________
Frequency ______________
18. A car travels in a circle with constant speed. The net force on the car will be in which
direction?
19. Marianne puts her favorite Backstreet Boys disc in her CD player. If it spins with a
frequency of 1800 revolutions per minute, what is the period of spin of the compact disc?
20. What is the radius of an automobile tire that turns with a frequency of 11 Hz and has a
linear speed of 20.0 m/s?
21. A cement mixer of radius 2.5 m turns with a frequency of 0.020 Hz. What is the centripetal
acceleration of a small piece of dried cement stuck to the inside wall of the mixer?
Universal Gravitation
22. What happens to the force between two masses if the distance between them is doubled?
23. What happens to the force between two masses if the distance between them is
quadrupled?
24. What happens to the force between two masses if the distance between them is cut in half?
25. What happens to the force between two masses if the mass of one object is doubled?
26. What happens to the force between two masses if the mass of both objects are doubled?
27. Two objects, each with a mass of 10 kg, are separated by a distance of 1 m. What is the force
between them?
28. Two objects, each with a mass of 10 kg, are separated by a distance of 2 m. What is the force
between them?
29. Two objects, each with a mass of 2 x 1012 kg, are separated by a distance of 1 x 106 m. What
is the force between them?
30. What is the force between a 30 kg mass and a 20 kg mass separated by a distance of 5 m?
31. Two objects each have a mass of 1 x 106 kg. The force between the objects is 200 N. What is
the distance between them?
Universal Gravitation Math Practice
32. Determine the force of gravitational attraction between the earth (m = 5.98 x 1024 kg) and a
70-kg physics student if the student is standing at sea level, a distance of 6.38 x 106 m from
earth's center.
33. Determine the force of gravitational attraction between the earth (m = 5.98 x 1024 kg) and a
70-kg physics student if the student is in an airplane at 40000 feet above earth's surface.
This would place the student a distance of 6.39 x 106 m from earth's center.
PROJECTILE MOTION PROBLEMS
1. A water balloon is launched and after 5 seconds lands 50 meters away. What is the horizontal
velocity of the water balloon?
2. A stone is thrown from the top of a cliff and lands 10.4 seconds later. How high is the cliff?
3. Janet jumps off a high diving platform with a horizontal velocity of 2.8 m/s and lands in the water
2.6 seconds later. How far away from the base of the platform does she land?
4. In the question above, what is Janet’s final velocity when she hits the water?
5. A cannon ball is fired from the top of a cliff and lands 15.6 seconds later? How high is the cliff?
6. In the question above, if the horizontal velocity is 8.5 m/s, how far from the base of the cliff
does the cannon ball land?
7. A toy car runs off the edge of a table that is 1.2 meters high, falls for 1.5 seconds and lands 0.4
meters away from the table. What is the horizontal velocity of the toy car?
8. In the question above, what is the final velocity of the toy car when it hits the floor?
Additional Projectile Motion Review
1) A _projectile_ is a thrown object. It follows a_curvilinear__ path.
2) Projectiles have a _constant__ horizontal velocity which means they cover _equal___ amounts of
distance in _equal__ amounts of time.
3) Projectiles _accelerate__ vertically due to _gravity__ which means they cover _different____
amounts of distance in equal amounts of time.
4) Projectiles that are launched and land at the same _elevation__ follow a _parabolic___ path. This
means the time _up_ equals the time _down__.
5) When solving projectile motion problems, the _horizontal__ velocity is constant so the only
formula needed is ___v = d/t_____.
6) When solving projectile motion problems, the_vertical___ velocity is changing so the formulas
used are __d = vit + 1/2gt2____ and __vf = vi + gt_____.
7) The launch _angle___ has an effect on the range or the _distance___ a projectile travels and the
_height____ or how high a projectile travels.
8) The range is at a maximum when the launch angle is _45__ degrees.
9) The motion of a spinning object is called _circular____ motion.
10) In circular motion, the _speed___ is constant but the _velocity__ is not because the _direction___ is
constantly changing.
11) The velocity vector is _tangent_ to the circle.
12) The acceleration vector is _perpendicular__ to the velocity vector and directed __towards the
center of the circle.
Problems:
20) A stone is thrown from the top of a cliff and lands 15.0 seconds later. How high is the cliff?
Givens:
Formula:
t = 15.0 sec
d = vit + 1/2gt2
g = 9.8 m/s2
Work:
vi = 0
Answer:
1102.5 m
Unknown:
d = (0)(15.0) + ½(9.8)(152)
d=?
21) A boy throws a football to his friend with a horizontal velocity of 5 m/s. If his friend catches it 8
seconds later, how far did the football move horizontally (ignore air resistance)?
Givens:
v = 5 m/s
t = 8 sec
Formula:
v = d/t
Answer:
40 m
Work:
5 m/s = d/8 sec
Unknown:
d = (5 m/s)(8 sec)
d=?
22) A platform diver does a swan dive off of a 10 meter platform. She lands in the water 3 seconds
later and she is 2 meters away horizontally from the platform. What is her horizontal velocity?
Givens:
Formula:
d=2m
v = d/t
t = 3 sec
Answer:
0.67 m/s
Work:
v = 2 m/3 sec
Unknown:
v=?
23) In the question above, what is her final vertical velocity when she lands in the water?
Givens:
t = 3 sec
Formula:
vf = vi + gt
vi = 0
Work:
g = 9.8 m/s2
vf = 0 + (9.8 m/s2)(3 sec)
Unknown:
vf = ?
Answer:
29.4 m/s