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Chapter 5 Review - Forces
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Please solve the following problems showing the formula, your number substitution, and your
circled final answer to the correct number of significant figures and with the proper units!
1. A force acts on a 2.0 kg mass and gives it an acceleration of 3.0 m / s 2 .
(a) How large is the force?
(b) What acceleration is produced by the same force when acting on a mass of:
(i) 1.0 kg
(ii) 4.0 kg
2. An 800.0 N person stands on a scale on the floor in an elevator. What is the scale reading if
the elevator has an acceleration of:
(a) 1.8 m / s 2 up
(b) 2.2 m / s 2 down
(c) 9.8 m / s 2 down
3. A cord passing over a frictionless pulley has a 4.0 kg ( m1 ) object tied to one end and a 12.0
kg ( m2 ) object tied to the other. Find the acceleration of the two masses and the tension in
the cord.
m1
m2
4. If a force of 270 N is required to start a 40.0 kg box moving across a concrete floor with
constant velocity, what is the coefficient of friction between the floor and the box?
5. A 52 N sled is pulled across a cement sidewalk at a constant speed. A horizontal force of
36 N is exerted. What is the coefficient of friction?
6. A 4500 kg helicopter accelerates upwards at 2.0 m / s 2 . What lift force is exerted by the air on
the propellers?
7. Two objects, a certain distance apart, have a mutual force of gravity of 60N.
a. What would the force of gravity be if the distance between the objects was doubled?
[Hint: Use algebra.]
b. What would the force of gravity be if the distance between the objects was halved?
c. What would the force of gravity be if the mass of one of the objects was tripled?
8. Suppose that the applied force has a magnitude of 420 N. If m1 = 12 kg, and the acceleration of
m1 is 5.2 m/s2 to the right,
a) What is the magnitude of the friction force?
b) What is the value of the coefficient of kinetic friction?
9. A 1400 kg vehicle is accelerated from rest to 16 m/s over a distance of 92 m. What is the
net force during this acceleration?
10. A motorbike and rider having a mass of 160 kg, coast to a stop in 51 meters. Their original
velocity was 15 m/s. What was the stopping force exerted by the road on the motorbike and
rider?
11. A 3.2 x 103 kg satellite is 2.4 x 106 m from the centre of the moon. What is the magnitude of
the moon’s gravitational force on the satellite? (1 mark)
12. Two objects, each with a mass of 8.0 x 102 kg produce a gravitational force between them of
3.7 x 10-6 N. What is the distance between them?
(2 marks)
13. Object A, with mass m1, is a distance d away from object B, of mass m2. This results in a
gravitational force of F. Suppose the mass of m1 is tripled, and moved three times further
away from m2 than it was originally. What is the gravitational force between the objects
now?
A. F/9
B.
F/3
C.
3F
D.
9F
14. The acceleration due to gravity on the surface of Mars is 3.8 m/s2. How much would a 6.3 kg
watermelon weigh on Mars?
15. The mass of Mars is 6.421 x 1023 kg. Use your answer from the above question and
Newton’s Law of Universal Gravitation to calculate the radius of Mars.
16. Consider the following diagram.
m1=3.0 kg
m2=6.0 kg
a) Draw a free body diagram showing the forces acting on m1.
b) Find the acceleration of the system.
Key Formulae: F  ma
Fg 
Gm1m2
r2
Data Values:
Mass
of Earth
Radius of Earth

Gravitational Constant
Acceleration of gravity on Earth’s Surface
Mass of Moon
Radius of Moon
Mass of Sun
Fg = mg
5.98 x 1024 kg
6.38 x 106 m
G = 6.67 x 10-11 Nm2/kg2
g = 9.8 m/s2
7.35 x 1022 kg
1.74 x 106 m
1.98 x 1030 kg