Homework Solutions
Chapter #1
1-5
If a car is traveling at 55 mph.
a) Determine its speed in kilometers per hour
Convert miles per hour to kilometers per hour
Known: 1 mile = 1.609 km
 miles  1.609km 
55mph =  55

 = 88.5 km h
 hour  1mile 
b) Determine its speed in meters per second
Known: 1 mile = 1609 m
 miles  1609m  1hour 
55mph =  55


 = 24.6 m s
 hour  1mile  3600 sec 
1-7
A rocket has mass of 250(103) slugs on earth.
a) Its mass in SI units
 14.5938kg 
 = 3.64845(10 6 )kg = 3.65Gg
250(10 3 ) slugs = 250(10 3 ) slugs 
 1Slugs 
b) Its weight in SI units
m
kg ⋅ m
We = mg = 3.64845(10 6 )kg (9.81 2 = 35.791(10 6 ) 2 = 35.8M
s
s
c) If the rocket is on the moon, where the acceleration due to gravity is gm = 5.30 ft/sec.
its weight in Si units
ft 

 4.4482 
6
Wm = mg m = 250(10 3 ) slugs  5.30 2  = 1.325(10 6 )lb 
 = 5.894(10 ) = 5.89 M
1
lb
s




(
)
[
[
]
]
[
]
d) If the rocket is on the moon, where the acceleration due to gravity is gm = 5.30 ft/sec.
its weight in Si units
m m = me = 3.65(10 6 )kg = 3.65Gg
1-10
What is the weight in Newton’s of an object that has a mass of:
a) 10kg
m

W =  9.81 2 (10kg ) = 98.1
s 

b) 0.5g

m
kg 

 = 4.90m
W =  9.81 2 (0.5 g )10 −3
g 
s 


c) 4.5Mg

m
kg 

 = 44.1k
W =  9.81 2 (4.5Mg )10 3
Mg 
s 


1-16
Two particles have a mass of 8kg and 12kg, respectfully. If they are 800mm apart,
determine the force of gravity acting between them. Compare the results with the weight
of each particle
mm
F = G 12 2
r
m3
Where G = 6.673(10 -11 )
kg ⋅ s 2
 8(12) 
F = 6.673(10 −11 ) 
== 10.0(10 −9 ) = 10.0n
2 
0
.
8


W1 = 8(9.81) = 78.5 W2 = 12(9.81) = 118 1-18
If a man weighs 155 lb on earth.
a)
Calculate his mass in slugs
Know
slug = lb•s2/ft




1
lb ⋅ s 2
W = 155lb
=
4
.
81
= 4.81Slugs

ft
ft
 32.2

s2 

b)
Calculate his mass in kilograms


 14.5938kg 
m = 155lb
 = 70.2kg
 32.2 ft 2 
s 

c)
Calculate his weight in Newton’s
W = 155(4.4482) = 689 d)
e)
If the man is on the moon, where the acceleration due to gravity is gm = 5.30.
Calculate his weight in pounds.
 5.30 ft 

s 2  = 25.5lb
W = 155lb

 32.2 ft 2 
s 

If the man is on the moon, where the acceleration due to gravity is gm = 5.30.
Calculate his mass in kilograms.


 14.5938kg 
m = 155lb
 = 70.2kg
 32.2 ft 2 
s 
