Physics Phy231 Exam 2 Section 2 Form D With Answers - Michigan State University Department Of Physics And Astronomy - Spring 2013 Page 3
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1
2
3Form D
Exam 2 PHY231 Spring 2013 Section 2
2.50 m/s
10.0 m/s
12. A 50.0-kg boy runs at a speed of
10.0 m/s and jumps onto a cart as
shown in the figure. The cart is
initially at rest. If the speed of the
cart with the boy on it is 2.50 m/s,
(
)
what is the mass of the cart?
= m
= m
+ m
p
v
; p
v
i
b
b
f
b
c
c
(
)
A) 100 kg
E) 210 kg
= p
⇒
+ m
= m
p
m
v
v
f
i
b
c
c
b
b
B) 125 kg
F) 260 kg
− v
m
(v
)
(50.0kg)(10-2.5)
C) 150 kg
G) 300 kg
b
b
c
=
=
= 150 kg
m
c
D) 175 kg
H) 165 kg
v
2.5
c
13. Complete the following statement: Momentum will be conserved in a two-body collision
only if
A) both bodies come to rest.
B) the collision is perfectly elastic
C) the kinetic energy of the system is conserved
D) the net external force acting on the two-body system is zero
E) the internal forces of the two body system cancel in action-reaction pairs
F) the internal forces have the same vector magnitudes and directions
G) the forces acting are non-conservative
H) the forces acting are conservative
14. A mother is holding her 4.5-kg baby in her arms while riding in a car moving at 22 m/s. The
car is involved in a head-on collision and stops within 1.5 seconds. What is the magnitude of the
force exerted by the baby on his mother's arms?
FΔp = Δp = mv
A) 45 N
E) 66 N
B) 90 N
F) 33 N
mv
(4.5kg)(22m/s)
C) 99 N
G) 57 N
F =
=
= 66 N
Δt
1.5s
D) 150 N
H) 80 N
15. The drawing shows two 4.5-kg balls located on the y-axis at 1.0 and 9.0 m, respectively,
and a third ball with a mass 2.3 kg which is located at 6.0 m. What is the location of the
center of mass of this system?
+ x
) + m
m
(x
x
A) 4.8 m
E) 6.4 m
1
1
2
3
3
=
x
cm
B) 5.2 m
F) 4.4 m
+ m
+ m
m
1
2
3
C) 5.6 m
G) 4.0 m
4.5kg(1.0 + 9.0)m + 2.3kg(6.0m)
D) 6.0 m
H) 0.0 m
=
= 5.2m
11.3 kg
16. A man with a mass of 100-kg and a
supply crate with a mass of 500-kg are on a frozen pond that is essentially frictionless. The initial
separation of the man and crate is a distance of 600 m. The man uses a very light rope to pull the
crate closer to him. How far has the
man moved when the crate reaches
+ m
m
x
x
c
c
m
m
=
= 0, x
= 600m
x
; x
him?
cm
c
m
+ m
m
c
m
A) zero m
E) 200 m
0 + 100kg(600m)
B) 90.0 m
F) 300 m
= 100m (touch at x
=
)
cm
C) 80.0 m
G) 400 m
600kg
D) 100 m
H) 500 m
Δx
= x
− x
= (100 − 600)m = −500m
m
m
cm
3
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