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Physics 11 Assignment
Dynamics – Chapters 4 & 5
Note: for all dynamics problem-solving questions, draw appropriate free body diagrams and
use the aforementioned problem-solving method.
1.
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Define the following terms:
Inertia
Dynamics
Mechanics
Newton’s Laws of Motion
Force
Inertial frame of reference
Non-inertial frame of reference
Mass
Inertial mass
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Gravitational mass
Contact force
Non-contact force
Weight
Static frictional force
Kinetic frictional force
Coefficient of friction
Normal force
Net force
2. Why does a child in a wagon seem to fall backward when you give the wagon a sharp pull?
3. If the acceleration of a body is zero, are no forces acting on it?
4. Why do you push harder on the pedals of a bicycle when first starting out than when moving at a
constant speed?
5. Only one force acts on an object. Can the object have zero acceleration? Can it have zero
velocity?
6. The force of gravity on a 2-kg rock is twice as great as that on a 1-kg rock. Why then doesn’t the
heavier rock fall faster?
7. A person exerts an upward force of 40 N to hold a bag of groceries. Describe the ‘reaction’ force
by stating (a) its magnitude, (b) its direction, (c) on what body it is exerted, and (d) by what body it
is exerted.
8. Why is the stopping distance of a truck much shorter than for a train going the same speed?
9. You can hold a heavy box against a rough wall and prevent it from slipping down by pressing only
horizontally. How can the application of a horizontal force keep an object from moving vertically?
10. a) A box sits at rest on a rough 30o inclined plane. Draw free body diagram, showing all the forces
acting on the box. b) How does the diagram change if the box were sliding down the plane? c)
How does the diagram change if the box were sliding up the plane?
11. What force is needed to accelerate a child on a sled (total mass = 60.0 kg) at 1.15 m/s 2?
12. A net force of 255 N accelerates a bike and rider at 2.20 m/s 2. What is the mass of the bike and
rider?
13. How much tension must a rope withstand if it is used to accelerate a 1050-kg car horizontally at
1.20 m/s2? Ignore friction.
14. What is the weight of a 66-kg astronaut (a) on Earth, (b) on the Moon (g = 1.7 m/s2), (c) on Mars
(g = 3.7 m/s2), and (d) in outer space traveling with constant velocity?
15. A 20.0-kg box rest on a table. (a) What is the weight of the box and the normal force acting on it?
(b) A 10.0-kg box is placed on top of the 20.0-kg box. Determine the normal force that the table
exerts on the 20.0-kg box and the normal force that the 20.0-kg box exerts on the 10.0-kg box.
16. What average force is required to stop an 1100-kg car in 8.0 s if it is traveling at 90 km/h?
17. What average force is needed to accelerate a 7.00-g pellet from rest to 175 m/s over a distance of
0.700 m along the barrel of a rifle?
18. A 10.0-kg bucket is lowered by a rope in which there is 63.0 N of tension. What is the
acceleration of the bucket? Is it up or down?
19. A person stands on a bathroom scale in a motionless elevator. When the elevator begins to
move, the scale briefly reads only 0.75 of the person’s weight. Calculate the acceleration of the
elevator and find the direction of acceleration.
20. If the coefficient of kinetic friction between a 35-kg crate and the floor is 0.30, what horizontal force
is required to move the crate at a steady speed across the floor? What horizontal force is required
if the coefficient of kinetic friction is zero?
21. A force of 40.0 N is required to start a 5.0-kg box moving across a horizontal concrete floor. (a)
What is the coefficient of static friction between the box and the floor? (b) If the 40.0-N force
continues, the box accelerates at 0.70 m/s2. What is the coefficient of kinetic friction?
22. An Atwood machine consists of masses 3.8 kg and 4.2 kg. What is the acceleration of the
masses? What is the tension in the rope?
23. The smaller mass on an Atwood machine is 5.2 kg. If the masses accelerate at 4.6 m/s 2, what is
the mass of the second object? What is the tension in the rope?
24. Stacie, who has a mass of 45 kg, starts down a slide that is inclined at an angle of 45° with the
horizontal. If the coefficient of kinetic friction between Stacie’s shorts and the slide is 0.25, what is
her acceleration?
25. You are shadowing a nurse in the emergency room of a local hospital. An orderly wheels in a
patient who has been in a very serious accident and has had severe bleeding. The nurse quickly
explains to you that in a case like this, the patient’s bed will be tilted with the head downward to
make sure the brain gets enough blood. She tells you that, for most patients, the largest angle that
the bed can be tilted without the patient beginning to slide off is 32.0° from the horizontal.
a. On what factor or factors does this angle of tilting depend?
b. Find the coefficient of static friction between a typical patient and the bed’s sheets.