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PHYS218 Spring15
Midterm Exam2
Physics 218: Midterm Exam2
March 25th, 2015
Please read the instructions below, but do not open the exam until told to do so.
Rules of the Exam:
1. You have 75 minutes to complete the exam.
2. Formulae are provided on a separate sheet. You may not use any other formula sheet,
handwritten, or printed materials.
3. You may use any SAT approved handheld calculator. However, you must show your
work to get credit.
4. The use of any communication devices like phone, radio, or iPod is strictly prohibited
during the exam.
5. Be sure to put a box around your final answers and clearly indicate your work.
6. Partial credit can be given only if your work is clearly explained and labeled. No credit
will be given unless we can determine which answer you are choosing, or which
answer you wish us to consider. If the answer marked does not follow from the work
shown, even if the answer is correct, you will not get credit for the answer.
7. You do not need to show work for the multiple choice questions.
8. If you need extra space, indicate/ mark on the main page of the problem that you are
continuing on another page.
9. Do not remove any pages from this booklet.
10. Have your TAMU ID ready when submitting your exam to the proctor.
Sign below to indicate your understanding of the above rules.
Full name (in CAPS): _____________________________________________________
UIN_______________________
Section Number: ______________________
Instructor’s Name:________________________
Your Signature: _______________________
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Short Problems (20)
__________
Problem 2 (20)
__________
Problem 3 (20)
__________
Problem 4 (20)
__________
Problem 5 (20)
__________
Total Score (100)
__________
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Problem 1 (20 points): Circle the correct option. No partial credit.
1.1 (5 points): The net force on a car moving at constant speed on a flat circular road is
a)
b)
c)
d)
e)
f)
g)
Zero.
Non zero, pointing to the direction of motion.
Non zero, pointing opposite to the direction of motion.
Non zero, pointing radially inward.
Non zero, pointing radially outward.
Non zero, parallel to velocity.
Non zero, vertically downward.
1.2 (5 points): An object at rest on a horizontal surface suddenly explodes in three equal mass fragments.
Immediately after explosion, two of the fragments move in the horizontal plane with equal speeds v at a 120o
angle between each other. What is the speed of the third fragment immediately after explosion?
a)
b)
c)
d)
e)
f)
g)
0
v/3
v/√3
v
√3 ∙ v
3∙v
None of the above
1.3 (5 points): The potential energy of a particle of mass m=0.10kg constrained to move on the x-axis is
U(x)=Ax2-Bx, where A=1.0N/m and B=4.0N. The particle starts from the point x=2.0m and has a negative total
energy E = - 3.0J. What are the positions (in meters) where the particle changes the direction of motion?
(Hint: The kinetic energy is zero at those positions).
a)
b)
c)
d)
e)
f)
g)
0.0 and 2.0
0.0 and 4.0
1.0 and 3.0
1.0 and 4.0
1.0 and 5.0
2.0 and 3.0
2.0 and 4.0
1.4 (5 points): A 4.00-kg block rests between the floor and a 3.00-kg block as shown in the figure. The 3.00-kg
block is tied to a wall by a horizontal rope. If the coefficient of kinetic friction is 0.800 between each pair of
surfaces in contact and force F=95.4N is applied to the lower block as shown in the figure, what is the tension
T in the rope when the 4.00-kg block starts moving?
a)
b)
c)
d)
e)
f)
g)
23.5 N
29.4 N
40.9 N
54.9 N
68.6 N
78.4 N
95.4 N
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Problem 2 (20 points)
Two spheres with masses m1 and m2 hang at rest at the ends of equal length strings. These two strings are
attached to the same point in the ceiling. The two spheres are released from equal heights h, as shown in the
figure. The two spheres, moving strictly in the plan of the figure, stick together after collision. Neglecting air
resistance, calculate in terms of m1, m2, and h:
a) The magnitude and direction of the velocity of the two spheres immediately after collision.
b) The height H reached by the two spheres moving together after their collision.
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Problem 3 (20 points)
A roller coaster car has the mass m when is fully loaded with passengers. The car moves along the frictionless
path shown in the figure. The radii of the circular segments are R1 and R2. The coaster starts from rest at the
initial height h. In terms of m, g, R1, and R2, calculate:
a) The maximum value of the height h such that the coaster would reach point B without flying from the
track? Justify your answer with a free body diagram.
b) For a known value of the height h, what is the magnitude and direction of the force exerted by the
track on the coaster at the point A? Justify your answer with a free body diagram.
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Problem 4 (20 points)
The figure below shows a box of mass m=2.0 kg on a ramp of angle θ=30o tied to a light rope passing over a
light pulley and attached to an ideal spring with constant k=20 N/m. The rope does not stretch or break. The
box is released from rest when the spring is unstretched. Once released, the box travels downward a
distance x=40 cm, where it stops and stays at rest. The coefficient of static friction between the ramp and the
block is µs and the coefficient of kinetic friction is µk . These coefficients are not given.
a) Use the work-energy theorem and the information provided to calculate the coefficient of kinetic friction µk
b) What is the magnitude and direction of the force of friction at the farthest point x=40 cm?
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Problem 5 (20 points)
Two blocks, connected together by a thin but strong cord, are placed on a ramp as shown in the figure. The
angle of the ramp is θ=45o, the masses of the blocks are mA=3.00kg and mB=1.00kg, and the coefficient of
static and kinetic friction between boxes and ramp are µs=0.400 and µk=0.400. The gravitational acceleration is
9.8m/s2. The mass of the cord is negligible; the cord does not stretch and does not break.
a) A force F is applied to the upper block as shown in the figure. Draw free body diagrams for the two
blocks.
b) The force F pulling up the ramp is 35.0N. Do the boxes move? If yes, what is the acceleration?
c) Given the force F=35.0N pulling up the ramp, calculate the tension in the cord.
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