Physics 1303 - Summer 1998
Homework Assignment #3
Due:Monday 29 June 1998
Chapters 5 and 6.
Chapter 5 - 6, 8, 9, 10, 17, 18, 19, 21.
Chapter 6 - 8, 12, 13.
Chapter 5 - 1, 18, 21, 26, 28, 32, 38, 39, 51, 65.
Chapter 6 - 1, 5, 6, 15, 27, 38A, 38, 51, 52.
I suggest that you try several unassigned problems, especially the ones
with corresponding figures, for practice.
These are the ANSWERS only, not the SOLUTIONS. It is not sufficient to
copy these and turn them in as homework. You must show your work.
Q 5-6) The scale measures the tension T in the cord attaching
the fish to the scale. This force is NOT equal to the force called
the weight W of the fish. In an inertial reference frame (a
non-accelerating frame), the magnitudes of these two distinct forces
are equal. But the elevator is accelerating; it is therefore not an
inertial reference frame, and the two forces T and W will not have the
- Remember that action-reaction paired forces NEVER act on the same
object. Gravity acts on the ball; this is the force of the Earth
pulling down on the ball. The reaction to this force is the
gravitational attraction of the ball pulling up on the Earth.
Both forces in this pair have the same magnitude and opposite
The normal force due to contact with the hand also acts on the ball.
This normal force prevents gravity from accelerating the ball.
The reaction to this force is the force of the ball on the hand;
this is the force that you feel, the way you know that a ball is
in your hand.
- Only the force of gravity due to the Earth acts on the ball as it
falls. The reaction force is the same as in part (a): the
gravitational attraction due to the ball acting on the Earth. The
Earth is so massive that the Earth's acceleration
aE=F/mE is hardly noticeable.
Q 5-9) No resultant (= net = total) force.
- Static friction between the crate and the truck bed.
- If the acceleration (or deceleration) of the truck is larger than
the largest possible force of static friction, then the crate will
slide. If the truck driver brakes, the crate may slide forward.
Q 5-17) Action-reaction paired forces NEVER act on the same object.
Q 5-18) 200 N (no, it is NOT 400 N!)
Q 5-19) The coefficient of static friction is larger than the
coefficient of kinetic friction.
Q 5-21) The 20-N rock is twice as massive, or in other words, twice
as hard to accelerate.
Q 6-8) The water will not spill as long as the pail accelerates
toward its open end faster than the water does. The acceleration
of the pail can be horizontal, vertical (up or down), or toward
the center of a circle.
Q 6-12) Driving in a circle at constant speed.
Q 6-13) Not possible.
- 0.75 m/s2
- (4 i + 3 j) m/s2 or 5 m/s2 at 36.9o
- (5.5 i + 2.6 j) m/s2 or 6.08 m/s2
- (2.5 i + 5 j) N
- 5.59 N
- T1=31.5 N
- T1=113 N
- 648 N each
- No, an infinite force is required.
- 217.8 N
P 5-38) a = F/(m1 + m2)
T = F m1/(m1 + m2)
P 5-39) The bug has a greater chance of surviving case (a).
P 5-51) 0.077 (no units)
- 8.0 m/s
- 3.02 N
P 6-5) 0 < v < 8.08 m/s
- 5.6 x 103 m/s
- 240 min = 14400 s
- 735 N
P 6-15) 3.13 m/s
- 491 N
- 50.1 kg
- 2 m/s2
- T=m2 g
- Tension T
- v = (m2 g r / m1 )1/2
- 9.8 N
- 9.8 N
- 6.3 m/s
- 1.58 m/s2
- 455 N
- 329 N
- 397 N at 9.15o tilted from the vertical toward the center
of the wheel
- 5.19 m/s
- 555 N
Please report any corrections to
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