RIII-
1. An elevator is going up at a constant speed. Near the top floor, it
starts to slow to a stop. During the period that it is slowing down,
its acceleration is
A) downward.
B) upward.
C) in some other direction.
Answer: Downwards
∆
v
v
1
v
2
RIII-
2. Consider the vectors
V
1
and
V
2
shown.
What is the direction of
∆
V
=
V
2
–
V
1
V
1
+
∆
V
=
V
2
v
1
direction of
∆
v?
D
v
2
C
A
B
Answer: B) down
RIII-
3. Consider the vector
A
G
y
Which equation is correct?
A) A
x
= +A cos
θ
A
θ
B) A
x
= –A cos
θ
C) A
x
= +A sin
θ
D) A
x
= –A sin
θ
x
Answer: A
x
= –A sin
θ
RIII-
4. A projectile is fired at an initial speed of v
o
at an angle of
θ
above the horizontal.
Which of the following expressions could possibly be the correct expression for the range
of the projectile? (Hint) check the units).

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(
)
(
)
2
0
o
2
o
2
o
A) x
2g v tan
B) x
2g v sin(2 )
v
g
C) x
sin 2
D) x
sin 2
g
v
=
θ
=
=
θ
=
θ
θ
Answer: C) only this expression has the units of distance
RIII-
5. A plane in horizontal flight moving at constant velocity drops a heavy package
while approaching the border of a kingdom.
Which crosses the border first?
(As usual,
assume that air resistance is negligible.)
A) the plane
B) the package
C) both cross at the same instant
v = constant
border
Answer: Both cross at the same instant.
RIII-
6. A boy of mass M = 50 kg
pushes on a baby carriage of mass M/5 = 10 kg.
The
force on the carriage from the boy has magnitude F
onCarriage
.
The force on the boy from
the carriage handle has magnitude F
onBoy
.
How do the forces compare?
A) F
onCarriage
= 5 F
onBoy
B) F
onCarriage
= 0.2 F
onBoy
C) F
onCarriage
= F
onBoy
Answer:
By Newton's third law, the forces must be the same magnitude (and opposite in
the direction).
RIII-
7. A heavy–duty truck pulling a light trailer is accelerating forward.
How does the
force on the truck F
onTruck
from the trailer compare to the force on the trailer F
onTrailer
from
the truck?