Download Which one of the following statement is true? a. the center of

Phys101
Term:131
Online HW-Ch09-Lec01
Q1:
Which one of the following statement is true?
a. the center of mass of an object must lie within the object
b. all the mass of an object is actually concentrated at its center of mass
c. the center of mass of an object cannot move if there is zero net force on the
object
d. the center of mass of a cylinder must lie on its axis
e. none of the above
Ans:
e
Q2:
A 1.0 kg particle is moving with a velocity of 16 m/s along the positive x direction
while a 3.0 kg particle is moving with a velocity of 4.0 m/s along the positive y
direction. Find the magnitude of their center of mass velocity?
Ans:
vx,com (m1 + m2 ) = m1 v1x + m2 v2x
vx,com =
=
m1 v1x + m2 v2x
m1 + m2
1.0 × 16 + 3.0 × 0
3+ 1
vx,com = 4 m/s
vy,com (m1 + m2 ) = m1 v1y + m2 v2y
vy,com =
m1 v1y + m2 v2y
1.0 × 0 + 3 × 4
=
m1 + m2
3+1
vy,com = 3 m/s
|v| = �vx,com 2 + vy,com 2 = �42 + 32 = 5 m/s
Q3:
Two boys, with masses of 40 kg and 60 kg, respectively, stand on a horizontal
frictionless surface holding the ends of a 10 m long massless rod. The boys pull
themselves toward each other along the rod. When they meet, what distance will the
60 kg boy have covered:
Ans:
Since there is no external force they will meet at com
Xcom (m1 + m2 ) = m1 x1 + m2 x2
Xcom (60 + 40) = 60 × 0 + 40 × 10
Xcom
400
=
=4m
100
KFUPM-Physics Department
com
m1
60 kg
m2
40 kg
1