Download 2d-forces-problems-2016

4/16/13
Forces in Two Dimensions (Sec 5-3)
(Equilibrium, Friction, Inclined planes, Massless, Forces at an Angle)
Equilibrium (Glencoe Chapter 5, Walker pg 146 – 148, 150 – 157)
Textbook problems: Glencoe pg 142 #95, 96, 97, 98. Walker pg 166 #16
1. A 300 N sign is supported by two ropes. The angle between the ropes is 30°. What is the tension in each
rope?
2. Two ropes supporting a sign each have a tension of 292 N. The angle between the ropes is 50°. What is the
mass of the sign?
Forces on Level Surfaces (Glencoe Ch 5, Walker pp 137 – 145)
Textbook Problems: Glencoe pg 142-143 #90, 91, 104 Walker pg 165 #4
3. A 125 N force causes a 50 kg box to move at a constant velocity. What is the force of friction, and the
coefficient of friction?
4. A 75 kg crate is pulled by a 900 N forward force along a surface where the coefficient of friction is 0.3.
What is the acceleration of the crate?
5. A 150 N force applied to a 70 kg box causes an acceleration of .3 m/s/s. What is the force of friction, and
the coefficient of friction?
6. A 60 kg box accelerates at 2 m/s/s along a surface where the coefficient of friction is 1.25. What is the
forward force?
7. A box that weighs 49 N is placed on a level surface which has a coefficient of friction of 0.50. A force of
40.5 N is applied to slide the box along the surface. Find the Force of friction, the net Force, and the
acceleration of the box.
Forces on Inclined Surfaces (Glencoe Sec 5-3, Walker pp 137 – 145)
Textbook Problems: Glencoe pg 143 #99. Walker pg 168 # 35,36
8. How much force is required to pull a 10 kg block up a 25º incline at a constant velocity? The coefficient of
friction is 0.5.
9. An 80 kg box is sliding at a constant velocity down a ramp set at a 30º angle. Find the Normal Force, the
Pulling Force of gravity, and the Force of Friction.
10. A 500 N box is accelerating down a 30º incline at 1.3 m/s/s despite being held back by a rope. If the
coefficient of friction between the box and the board is 0.25, what is the tension in the rope?
11. A 200 lb box rests on an incline of 35 to the horizontal. The coefficient of friction between the surfaces is
0.40. What is the force necessary to move the box up the plane at a constant velocity? Ignore static friction.
12. A 100 N box rests on an incline of 35 to the horizontal. The coefficient of friction between the two surfaces
is 0.50. Find the force necessary to move the box up AND down the plane. Ignore static friction.
13. A 1000 N safe is to be lowered at constant speed down a plank into a waiting truck. The engine of the truck
is running. The plank is 6.0 m long and is 2.0 m higher at the upper (obviously) end. If the coefficient of sliding
friction is 0.30, will the safe need to be pushed down the plane or held back? How much force is needed?
14. A 70 kg box slides down a 26º incline with an acceleration of 2 m/s/s. Determine the coefficient of friction
between the surfaces.
15. A 3.00 kg wooden box slides from rest down a 35.0 wooden inclined plane. How long does it take the box
to reach the bottom of the 4.75 m wood incline? See table 5-1 on page 129 for the coefficient of friction.
16. A 65.0 kg crate is to be accelerated at 7.00 m/s/s up an incline plane making a 25.0 angle with the
horizontal. If the coefficient of friction between the crate and the incline is 0.200, how much force is required?
17. A 2000 N box is pulled up a 35° inclined plane where the coefficient of friction is 0.40. What force must
be applied? Ignore static friction.
18. A box accelerates down an inclined plane with a net force of 3.00 N. The coefficient of friction is 0.31 and
the force of friction is 17.11 N. What is the angle of incline?
Massless Problems (Walker pp 137 – 145)
Textbook Problems: Walker pg 165 #11 pg 169 #54
19. A box slides down a frictionless incline with an acceleration of 3.5 m/s/s. What is the angle of incline?
20. Find the acceleration of a cart on a frictionless incline set at 20
21. Find the angle of a frictionless track given the acceleration of a cart is 8.2 m/s/s.
22. A box slides down a 17 inclined plane at a constant velocity. What is the coefficient of friction?
23. The coefficient of friction between two surfaces is 2.5. What is the maximum angle of incline before the
object starts to slide?
24. A box slides down a 35 incline with an acceleration of 4.5 m/s/s. Find the coefficient of friction.
25. A box accelerates down a 50 inclined plane where the coefficient of friction is 0.20. Determine the
acceleration.
26. If you just slide down a 30 roof at uniform speed, what is the coefficient of friction between you and the
roof?
27. If the coefficient of friction between a set of waxed skis and the snow is 0.10, at what angle will a 90.0 kg
skier move at a constant speed down the slope?
28. A carpenter drops his hammer as he is shingling a roof. The hammer slides slowly and tantalizingly down
the freshly shingled roof at a uniform speed. The roof has a 45 % slope. Find the coefficient of friction. (A 45%
slope means the roof rises 4.5 feet for every 10 feet of horizontal distance.)
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Applied Forces at an Angle to Surface (Walker pp 126 – 129)
Textbook Problems: Walker pg 165 # 7, 8
29. The coefficient of sliding friction between a block and floor is 0.30. If the block is pushed at constant
velocity with a force of 100 N and acts at an angle of 37 above the horizontal, find the weight of the box.
30. A 40 kg sled is pulled with a constant velocity by a rope that makes an angle of 25º with the horizontal.
The tension in the rope is 100 N. Determine the coefficient of friction.
31. A 40 kg mower is pushed with a constant velocity by a force of 100 N which makes an angle of 35º with
the horizontal. Determine the coefficient of friction.
32. A 15 kg box is pulled on a level surface by a rope that makes a 60 angle with the horizontal. The tension
in the rope is 75 N. The box accelerated at 1.133 m/s/s. Find the coefficient of friction.
33. The lady of the house requests her 8 lb pet Pekinese to go out-of-doors. The Peke refuses. The lady applies a
broom to the unhappy mongrel. The broom handle makes an angle to the floor of 30 and she knows the
coefficient of friction between the dog and floor to be 0.60. Therefore, she can calculate the force along the
broom handle required to send the dog out the door. The speed along the floor is uniform (fast!). Calculate the
force along the handle.
34. A man is pushing a 60 lb box along a level floor with a uniform velocity of 4 ft/sec. He is exerting a force
on the box at an angle of 30 downward from the horizontal. The coefficient of friction between the sliding
surfaces is 0.25. Find the magnitude of his applied force.
35. A 146 N force is used to pull a 350 N wood block at a constant speed by a rope making an angle of 50.0
with the floor. Find the coefficient of sliding friction.
36. A 3 kg toy baby carriage is pushed along a level sidewalk by exerting a force of 50.0 N on the handle,
which makes an angle of 60.0 with the horizontal. What is the coefficient of friction between the carriage and
the sidewalk?
37. A 500 N box is pulled along a level floor with a rope that makes a 30º angle with the horizontal. The
tension in the rope is 200 N and the coefficient of friction is 0.25. Find the acceleration of the box.
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