Homework 5

Homework 5

PHYS2425, section 001, Spring 2016

Instructor: Dave Van Domelen
Current Score : 1 / 10 Due : Tuesday, February 23 2016 11:59 PM CST
1. 1/1 points | Previous AnswersSerPSE9 7.P.009.WI.
For = 2 + 4 – 5 , = -4 + 5 + , and = 5 – 3 , find · ( – ).
13
2. 0/1 points | Previous AnswersSerPSE9 7.P.010.
Find the scalar product of the vectors in the figure below, where ? = 121° and F = 34.0 N.
578.07
Your response differs significantly from the correct answer. Rework your solution from the beginning
and check each step carefully. J
WebAssign
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3. –/1 pointsSerPSE9 7.P.014.MI.FB.
The force acting on a particle varies as shown in the figure below. (The x axis in the graph is marked
in increments of 5.00 m.)
Find the work done by the force on the particle as it moves across the following distances.
(a) from x = 0 m to x = 20.00 m
J
(b) from x = 20.00 m to x = 30.00 m
J
(c) from x = 0 m to x = 30.00 m
J
4. –/1 pointsSerPSE9 7.P.019.
An archer pulls her bowstring back 0.436 m by exerting a force that increases uniformly from zero to
223 N.
(a) What is the equivalent spring constant of the bow?
N/m
(b) How much work does the archer do on the string in drawing the bow?
J
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5. –/1 pointsSerPSE9 7.P.028.
A 150-g bullet is fired from a rifle having a barrel 0.660 m long. Choose the origin to be at the
location where the bullet begins to move. Then the force (in newtons) exerted by the expanding gas
on the bullet is 16000 + 10000x – 24000×2, where x is in meters.
(a) Determine the work done by the gas on the bullet as the bullet travels the length of the
barrel. (Enter your answer to at least two decimal places.)
kJ
(b) If the barrel is 0.90 m long, how much work is done? (Enter your answer to at least two
decimal places.)
kJ
(c) How does this value compare with the work calculated in part (a)?
percent error = %
6. –/1 pointsSerPSE9 7.P.042.WI.
A 330-N child is in a swing that is attached to a pair of ropes 1.80 m long. Find the gravitational
potential energy of the child–Earth system relative to the child’s lowest position at the following
times.
(a) when the ropes are horizontal
J
(b) when the ropes make a 25.0° angle with the vertical
J
(c) when the child is at the bottom of the circular arc
J
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7. –/1 pointsSerPSE9 7.P.046.
A particle moves in the xy plane as shown in the figure below and experiences a friction force with
constant magnitude 3.03 N, always in the direction opposite the object’s velocity. Calculate the work
that you must do to slide the object at constant speed against the friction force as the object moves
along the following paths.
(a) the purple path O to followed by a return purple path to O
J
(b) the purple path O to followed by a return blue path to O
J
(c) the blue path O to followed by a return blue path to O
J
(d) Each of your three answers should be nonzero. What is the significance of this
observation?
The force of friction is a nonconservative force.
The force of friction is a conservative force.
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8. –/1 pointsSerPSE9 8.P.014.MI.FB.
A crate of mass 9.8 kg is pulled up a rough incline with an initial speed of 1.44 m/s. The pulling force
is 110 N parallel to the incline, which makes an angle of 21.0° with the horizontal. The coefficient of
kinetic friction is 0.400, and the crate is pulled 4.98 m.
(a) How much work is done by the gravitational force on the crate?
J
(b) Determine the increase in internal energy of the crate–incline system owing to friction.
J
(c) How much work is done by the 110-N force on the crate?
J
(d) What is the change in kinetic energy of the crate?
J
(e) What is the speed of the crate after being pulled 4.98 m?
m/s
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9. –/1 pointsSerPSE9 8.P.015.WI.
A block of mass m = 2.00 kg is attached to a spring of force constant k = 540 N/m as shown in the
figure below. The block is pulled to a position xi = 5.70 cm to the right of equilibrium and released
from rest.
(a) Find the speed the block has as it passes through equilibrium if the horizontal surface is
frictionless.
m/s
(b) Find the speed the block has as it passes through equilibrium (for the first time) if the
coefficient of friction between block and surface is µk = 0.350.
m/s
10.–/1 pointsSerPSE9 8.P.022.WI.
The coefficient of friction between the block of mass m1 = 3.00 kg and the surface in the figure below
is µk = 0.405. The system starts from rest. What is the speed of the ball of mass m2 = 5.00 kg when
it has fallen a distance h = 1.65 m?
m/s
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