Dynamics Unit Review
Name:……………………………..
Date:……………………………..
1. Circle T: True, or F: False. Rewrite each false statement to make it true.
(a) The force of friction is an electromagnetic force.
T
or
F
(b) The mathematical expression FA on B = –FB on A is a
statement of Newton’s first law.
T
or
F
(c) If the forces acting on a body are unbalanced, the body
will accelerate in the direction of the unbalanced force.
T
or
F
(d) An object's inertia is directly related to its size.
T
or
F
(e) The acceleration due to gravity is greater at Earth's
equator than at the Poles.
m
(f) 1 N  1 kg 2
s
T
or
F
T
or
F
(g) Gravity is a non-contact force.
T
or
F
(h) A free body diagram shows all action and reaction
forces on an object.
T
or
F
(i) The force of friction is directly proportional to the
normal force.
T
or
F
(j) The coefficient of static friction is usually smaller than
the coefficient of kinetic friction.
T
or
F
(k) The force of gravity on an object is equal to the
acceleration due to gravity.
T
or
F
Answers: [T;F;T;F;T;T;T;F;T;F;F]
2. Earth pulls down on a person with a force of 700 N. Write a description of the reaction force.
3. A child pulls a wagon of mass 20.0 kg, giving it a horizontal acceleration of 2.5 m/s 2[E]. If the wagon's handle makes an
angle of 300 with the horizontal and a 7.0 N[W] friction force exists, calculate the force with which the child is pulling on the
handle of the wagon. Draw a free body diagram. [65.8 N.]
4. (a) Find the acceleration of the system of boxes shown below (ignore friction). [2.5m/s/s [E].]
(b) Find the force exerted by box A on box B (ignore friction).[ 37.5 N[E]]
Dynamics Unit Review
Name:……………………………..
Date:……………………………..
5. A subway train has three cars, each with a mass of 12 000 kg. The frictional force on
each car is 1000 N.The first car, acting as an engine, exerts a horizontal force of 50 000 N[E] on the rails.
(a) What is the acceleration of the train? [1.31 m/s2[E].]
(b) What is the tension in the coupling between the first and second cars? [33 300 N.]
(c) What is the tension between the second and third cars? [16 700 N.]
6. A 40.0 kg object is being acted on simultaneously by a 110.0 N[E60 0N] force, a 40.0 N[S] force, and finally, a 50.0
N[E270S] force.
(a) Find the resultant force (net force) acting on the object, and its acceleration.[ 104.7 N[E18°N]; 2.6 m/s2[E18°N].]
(b) What is the object's velocity after 7.0 s, assuming that it started from rest? [18.3 m/s[E18°N].]
7. Briefly explain the following situations by referring to any of Newton’s laws.
(a) Posts and overhead rails are provided on buses for standing passengers to hold.
(b) It takes longer to accelerate a truck than a car from 0 to 100 km/h.
answer:
(a) Newton’s first law: If the standing passengers are not holding onto a post or railing, they will tend to continue travelling
forward when
the bus comes to a stop or fall backward if the bus accelerates from rest.
(b) Newton’s first or second law: Since the truck has more mass, it has more inertia and a greater force is required to accelerate it.
8. Three toboggans are connected by ropes as shown below. They are pulled across ice by a 600 N[E] force. There is no
friction.
(a) Calculate the tension in the rope between the 70 kg toboggan and the 50 kg toboggan. Draw a free body diagram. (Hint:
First find the acceleration of the system.) [280 N.]
(b) Find the tension in the rope between the 50 kg toboggan and the 30 kg toboggan. Draw a free body diagram.[480 N.]
(c) Draw a free body diagram of the 50 kg toboggan (showing all forces) and determine the net force on the 50 kg
toboggan.[ 200 N[E].]