Physics 20 Unit 2: Dynamics
1
Physics 20

STA
Work Booklet
Unit I
I
–
Dynamics
Chapter
4
–
Gravitational
Forces
Name: ______________________________________________________________________________
Physics 20 Unit 2: Dynamics
2
4.1 Gravitational Force due to Earth
1.
In a vacuum, a feather and a bowling ball are released from rest at the same time from the
same height. Compare the time it takes for each object to fall. Explain your answer.
2.
The Moon exer
ts a gravitational force that
is about
1/6
that exerted by Earth. Explain
why the mass of an object measured on the Moon using a balance is the same as if the object
were on Earth’s surface.
3.
The table below shows the magnitude of the gravitational force on objects of different mass in
Banff, Alberta.
(a) Graph the data.
(b) Calculate the slope of the line.
(c) What does the slope represent?
Physics 20 Unit 2: Dynamics
3
4.
How could you distinguish between a 5.0

kg medicine ball and a basketball in outer space
without looking at both objects?
5.
6.
Physics 20 Unit 2: Dynamics
4
4.2 Newton’s Law of Universal Gravitation
1.
Mars has two moons, Deimos and Phobos, each named after an attendant of the Roman war
god Mars. Deimos has a mass of 1.8
x
10
15
kg and its mean distance from Mars is 2.3
x
10
7
m.
Phobos has a mass of 1.1
x
10
16
kg and its mean distance from Mars is 9.4
x
10
6
m.
(a) Without doing any calculations, predict which moon will exert a greater gravitational force
on Mars. Explain your reasoning.
(b) Check your prediction in part
(a) by calculating the magnitude of the gravitational force
exerted by each moon on Mars. Mars’ mass is 6.42
x
10
23
kg. Show complete solutions.
[Deimos: 1.9 x 10
14
N Phobos: 5.3 x 10
15
N]
2.
3.
Physics 20 Unit 2: Dynamics
5
4.
5.
6.
7.
Physics 20 Unit 2: Dynamics
6
8.
The Moon has a mass of 7.35
x
10
22
kg and its equatorial radius is 1.74
x
10
6
m. Earth’s mass
is 5.97
x
10
24
kg and its equatorial radius is 6.38
x
10
6
m.
(a) Calculate the magnitude of the gravitational force exerted by
(i) the
Moon on a 100

kg astronaut standing on the Moon’s surface
[162N]
(ii) Earth on a 100

kg astronaut standing on Earth’s surface.
[978N]
(b) Explain why the values of F
g
in part (a) are different.
9.
10.
Physics 20 Unit 2: Dynamics
7
4.3 Gravitational Field
Strength
1.
Determine the
gravitational field at point P, 25.0 m away from a 50 kg mass as shown in the
diagram below. [5.34 x 10

12
N/kg to the left]
2.
Determine the
gravitational field at point P produced from two 50 kg masses as shown in the
di
agram below. [1.7 x 10

10
N/kg to the left]
3.
At the top of Mount Robson in British Columbia, a 7.5

kg turkey weighs 73.6 N [down].
Calculate the magnitude of the gravitational field strength at this location.
[9.8 N/kg down]
4.
Physics 20 Unit 2: Dynamics
8
5.
6.
7.
8.
Physics 20 Unit 2: Dynamics
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9.
10.
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