Answers needed to check Homework.

From: Gl4di4tor (fstanicziee_at_gmail-dot-com.no-spam.invalid)
Date: 03/01/05 

Date: 28 Feb 2005 23:35:06 -0600

I have all these questions due for Homework by Friday’s Physics 203
class, we get graded on the Homework so I need to get the correct
answers and the work that led to my answer. Since my textbook
doesn’t have the answer’s I was hoping you guys could help me out.
I’m only asking for the answers just so that I know I did the work
correctly. Thanks. Here are the questions.

FORCES AND NEWTONS LAWS OF MOTION:

19. On earth, two parts of a space probe weigh 11 000 N and 3400 N.
These parts are separated by a center-to-center distance of 12 m and
may be treated as uniform spherical objects. Find the mag¬nitude of
the gravitational force that each part exerts on the other out in
space, far from any other objects.

20. A rock of mass 45 kg accidentally breaks loose from the edge of a
cliff and falls straight down. The magnitude of the air resistance
that opposes its downward motion is 250 N. What is the magnitude of
the acceleration of the rock?

24. The drawing (not to scale) shows one alignment of the sun, earth,
and moon. The gravitational force FsM that the sun exerts on the moon
is perpendicular to the force FEM that the earth exerts on the moon.
The masses are: mass of sun = 1.99 X 1030 kg, mass of earth = 5.98 X
1024 kg, mass of moon = 7.35 X 1022 kg. The dis¬tances shown in the
drawing are rsM = 1.50 X 10" m and rEM = 3.85 X 108 m. Determine the
magnitude of the net gravitational force on the moon.

37. A block whose weight is 45.0 N rests on a horizontal table. A
horizontal force of 36.0 N is applied to the block. The coefficients
of static and kinetic friction are 0.650 and 0.420, respectively.
Will the block move under the influence of the force, and, if so,
what will be the block's acceleration? Explain your reasoning.

38. A cup of coffee is sitting on a table in an airplane that is
flying at a constant altitude and a constant velocity. The
coefficient of static fric¬tion between the cup and the table is
0.30. Suddenly, the plane acceler¬ates, its altitude remaining
constant. What is the maximum acceleration that the plane can have
without the cup sliding backward on the table?

47. A supertanker (mass =
1.70 X 108 kg) is moving with
a constant velocity. Its engines
generate a forward thrust of 7.40 X 105 N. Determine (a) the
magni¬tude of the resistive force exerted on the tanker by the water
and (b) the magnitude of the upward buoyant force exerted on the
tanker by the water.

* 43. ssm A skater with an initial speed of 7.60 m/s is gliding across
the ice. Air resistance is negligible. (a) The coefficient of kinetic
friction between the ice and the skate blades is 0.100. Find the
de¬celeration caused by kinetic friction. (b) How far will the skater
travel before coming to rest?

63. Only two forces act on an object (mass = 4.00 kg), as in the
drawing. Find the magni¬tude and direction (relative to the x axis)
of the acceleration of the object.

* 58. A mountain climber, in the process of crossing between two
cliffs by a rope, pauses to rest. She weighs 535 N. As the drawing
shows, she is closer to the left cliff than to the right cliff, with
the re¬sult that the tensions in the left and right sides of the rope
are not the same. Find the tensions in the rope to the left and to the
right of the mountain climber.

66. A falling skydiver has a mass of 110 kg. (a) What is the
magni¬tude of the skydiver's acceleration when the upward force of
air re¬sistance has a magnitude that is equal to one-third of his
weight? (b) After the parachute opens, the skydiver descends at a
constant veloc¬ity. What is the force of air resistance (magnitude
and direction) that acts on the skydiver?

69. ssm www A student is skateboarding down a ramp that is 6.0 m long
and inclined at 18° with respect to the horizontal. The initial speed
of the skateboarder at the top of the ramp is 2.6 m/s. Neglect
friction and find the speed at the bottom of the ramp.
tension force? (b) How much work is done if the same tension is
di¬rected parallel to the snow?
[b:400e1f0e10]
WORK AND ENERGY[/b:400e1f0e10]

4. A 75.0-kg man is riding an escalator in a shopping mall. The
es¬calator moves the man at a constant velocity from ground level to
the floor above, a vertical height of 4.60 m. What is the work done
on the man by (a) the gravitational force and (b) the escalator?

3. A person pulls a toboggan for a distance of 35.0 m along the snow
with a rope directed 25.0° above the snow. The tension in the rope is
94.0 N. (a) How much work is done on the toboggan by the tension
force? (b) How much work is done if the same tension is directed
parallel to the snow?

15. When a 0.045-kg golf ball takes off after being hit, its speed is
41 m/s. (a) How much work is done on the ball by the club? (b)
As¬sume that the force of the golf club acts parallel to the motion
of the ball and that the club is in contact with the ball for a
distance of 0.010 m. Ignore the weight of the ball and determine the
average force applied to the ball by the club.

7. A person pushes a 16.0-kg shopping cart at a constant velocity for
a distance of 22.0 m. She pushes in a direction 29.0° below the
horizontal. A 48.0-N frictional force opposes the motion of the cart.
(a) What is the magnitude of the force that the shopper exerts?
De¬termine the work done by (b) the pushing force, (c) the frictional
force, and (d) the gravitational force.

18. Interactive LearningWare 6.2 at www.wiley.com/college/ cutnell
provides a useful review of the concepts that play a role in this
problem. A 5.0 X 104-kg space probe is traveling at a speed of 11 000
m/s through deep space. Retrorockets are fired along the line of
motion to reduce the probe's speed. The retrorockets generate a force
of 4.0 X 10 5N over a distance of 2500 km. What is the final speed of
the probe?

* 20. A 16-kg sled is being pulled along the horizontal snow-covered
ground by a horizontal force of 24 N. Starting from rest, the sled
at¬tains a speed of 2.0 m/s in 8.0 m. Find the coefficient of kinetic
fric¬tion between the runners of the sled and the snow.

26. A 0.60-kg basketball is dropped out of a window that is 6.1 m
above the ground. The ball is caught by a person whose hands are 1.5
m above the ground. (a) How much work is done on the ball by its
weight? What is the gravitational potential energy of the basketball,
relative to the ground, when it is (b) released and (c) caught? (d)
How is the change (PEf — PEo) in the ball's gravitational potential
energy related to the work done by its weight?

29. A 75.0-kg skier rides a 2830-m-long lift to the top of a
moun¬tain. The lift makes an angle of 14.6° with the horizontal. What
is the change in the skier's gravitational potential energy?

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