ID CODE: B Physics 201 Midterm Exam 2 October 27

ID CODE: B
Physics 201 Midterm Exam 2
October 27th, 2014
Name: ............................................... Student ID: .........................
Section: .........................
TA (please circle):
Jonathan Brown
Steven Casper
Yu Huang
Benjamin Lemberger
Patrick Vanmeter
Nicole Vassh
Brandon Wilson
Instructions:
1. Donʼt forget to write down your name, student ID#, and section number. You need do
this on (this page of) your test book and on your Scantron sheet as well.
2. Answer all multiple choice questions in this test book by indicating the best answer
among choices. You must do this both on your test book and on your Scantron sheet.
Follow instructions on the Scantron sheet on how to mark valid answers.
3. When you finish, you need to turn in both this test book and the Scantron sheet.
4: Use the blank side of question pages as additional draft spaces. An extra blank sheet
is provided at the end of the test book.
5: Only one answer is allowed per problem/question. All problems have equal weight.
Constants: g=9.8 m/s2
(Note: Neglect air friction for all projectile motion).
Please be very careful with the first question even though the answer will not count
towards your grade:
1. ENTER THE ID CODE ABOVE IN THE UPPER RIGHT CORNER
A. ID Code A
B. ID Code B
C. ID Code C
D. ID Code D
E. ID Code E
2. Consider a process in which a wood block is moving up along a slope. The block is
subject to four forces: its weight, the normal force from the slope, the kinetic friction
and a non-conservative pushing force. It is known that in the process the work done
by its weight is -40J, by the pushing force is 70J, and by the friction is -20J. Which
of the following statements is true regarding the block-earth system’s energies at the
end of this process?
a.
b.
c.
d.
e.
the system’s kinetic energy increases but its mechanic energy decreases.
the system’s kinetic energy decreases but its mechanic energy increases.
both its kinetic and mechanic energy decrease.
both its kinetic and mechanic energy increase.
None of above is true.
3. The systems shown below are in equilibrium with m = 1.70 kg. The spring scale is
calibrated in newtons, what does it read? Ignore the masses of the pulleys and strings
and also ignore all frictions.
a.
b.
c.
d.
e.
1.7 N
16.7 N
33.4 N
3.4 N
none of above is within 5% from the correct answer.
4. A car of 100 kg on a frictionless roller coaster track is sliding down from height of
10m to the ground. What is the total work done on the car during this 10m
descending? (ignore all friction).
a.
b.
c.
d.
e.
Zero
9.8 kJ
-9.8 kJ
4.9 kJ
None of above is within 0.5 kJ of the correct answer.
5. The gravitational force exerted on a baseball is 2.24 N down. A pitcher throws the
baseball horizontally with velocity 14.0 m/s by uniformly accelerating it along a
straight horizontal line for a time interval of 187 ms. The ball starts from rest. What is
the direction of the force the pitcher exerts on the ball?
a.
b.
c.
d.
e.
7.5o above the horizontal
15o above the horizontal
23o above the horizontal
0o , i.e. horizontally
None of above is within 10% of the correct answer.
6. An object is observed to have an acceleration in a direction θ = 54.5° east of north.
The figure below shows a view of the object from above. The force F2 acting on the
object has a magnitude of 6.10 N and is directed north. Determine the magnitude of
the force F1 acting on the object
a.
b.
c.
d.
e.
8.6 N
11.3 N
4.7 N
none of above is within 0.2 N from the correct answer.
It cannot be determined as neither the mass nor the magnitude of the acceleration
is given.
7. A bead of m=4.6 g slides without friction around a loop–the–loop (see figure below).
The bead is released from rest at a height h.
a.
b.
c.
d.
e.
If h= 3.70R, How large is the normal force on the bead at point “A” ?
0.11 N
0.045 N
0.24 N
none of above is within 5% from the correct answer.
Not enough information as the value of R is not given.
8. Two blocks, each of mass m are hung from the ceiling of an elevator as in the figure
below. The elevator moves with an upward acceleration.
What can we say about the tensions T1 and T2 in comparison?
a.
b.
c.
d.
e.
T1= 2T2
2T1= T2
T1= T2
Can not be determined as the magnitude of the acceleration is not given
None of above is correct.
9. Still with the above setting, it is known that the mass of each block is 3.45 kg. If the
strings can withstand a maximum tension of 86.6 N, what maximum acceleration can
the elevator have before a string breaks?
a.
b.
c.
d.
e.
9.8 m/s2
7.2 m/s2
1.3 m/s2
2.8 m/s2
None of above is with 5% from the correct value.
10. A coin placed 29.6 cm from the center of a rotating horizontal turntable starts to slip
when its speed is 50.2 cm/s. What is the coefficient of static friction between coin and
turntable?
a. 0.065
b. 0.087
c. 0.283
d. 0.387
e. none of above is within 0.005 from the correct answer.
11. Two blocks of mass m1 = 2.00 kg and m2 = 6.50 kg are connected by string that
passes over a pulley (see the figure below). The string is massless and inextensible.
Initially, the blocks are held still by an external force and after the external force is
removed, the blocks start to move. What is the acceleration of m1 when it is moving?
(Ignore all frictions)
a.
b.
c.
d.
e.
1.53 m/s2 up slope
1.53 m/s2 down slope
2.98 m/s2 up slope
2.98 m/s2 down slope
None of above is within 10% from the correct answer.
12. In the setting above, consider the Blocks-Earth system. As the blocks are moving,
what can we say about the system’s energies?
a. The system’s potential energy increases but the system’s mechanic energy remains
unchanged.
b. The system’s potential energy decreases but the system’s mechanic energy remains
unchanged.
c. Both the system’s potential and mechanic energy remain unchanged.
d. Both the system’s potential and mechanic energy increase.
e. Both the system’s potential and mechanic energy decrease.
13. A car of a total mass 1200 kg (including passengers) is climbing up a slope of 18o at a
constant speed of 5.0 m/s. What is the (minimum) power its engine has to provide to
maintain this speed?
a.
b.
c.
d.
e.
7.3 kW
9.5 kW
14.7 kW
18.2 kW
none of above is within 0.2kW from the correct answer.
14. A particle of mass M, attached by a string with one fixed end at center C, is
undergoing a circular motion on a smooth horizontal table. (See left figure below for
a top view). At the moment when the particle is passing the point B, the string is
suddenly cut at the cutting point x as shown in the right figure above. Viewing from
the top, which is the trajectory of the particle after the cut?
a. Still the same circular course as shown by dashed trajectory 1 in the right figure
above.
b. A less curved course as shown by dashed trajectory 2.
c. A straight-line tangent to the original circle (dashed trajectory 3.)
d. The trajectory will now bend outwards due to the original circular inertia (dashed
trajectory 4)
15. Two children stand on a platform at the top of a curving slide next to a backyard
swimming pool. They decide to get into water in different way. The bigger (and
heavier) child chooses to slide on through the frictionless slide, and the smaller child
simply hops off to jump straight down into the pool. Upon reaching the water,
a.
b.
c.
d.
e.
The bigger kid has higher kinetic energy and higher speed.
The bigger kid has higher kinetic energy but lower speed.
The bigger kid has lower kinetic energy but higher speed.
Both kids have the same kinetic energy and the same speed.
None of above is true.
16. A block M = 0.93 kg is pulled up along an inclined plane by a constant force F. The
coefficient of kinetic friction between the block and the plane surface µk=0.30. The
block starts from rest at the bottom. The block’s speed is 7.38 m/s when it reaches
the top. How big is the force F?
(hint: you can use Newton’s 2nd law, but an energy approach would be easier.)
a.
b.
c.
d.
e.
18.4N
12.1 N
16.7 N
22.3 N
none of above is within 0.3N from the correct answer.
17. The figure below shows the speed of a person's body as he does a chin-up. Assume
the motion is vertical and the mass of the person's body is 69.2 kg. what is (the
magnitude of) the force exerted by the chin-up bar on his body at t=1.5s.
a.
b.
c.
d.
e.
3474 N
720 N
678 N
637 N
none of above is within 5% from the correct answer.
18. A block is set into motion up an inclined plane with an initial speed of vi = 7.80 m/s.
The block comes to rest after traveling d = 3.00 m along the plane, which is inclined
at an angle of θ = 18.0° (figure below). What is the coefficient of kinetic friction
between the block and the plane surface?
(hint: you can use Newton’s 2nd law, but an energy approach would be easier.)
a.
b.
c.
d.
e.
0.34
0.26
0.62
0.48
none of above is within 5% from the correct answer.
19. An object of mass m = 0.570 kg is suspended from the ceiling of an accelerating truck
as in the figure below. Take a = 2.40 m/s2. Find the angle θ that the string makes with
the vertical.
a.
b.
c.
d.
e.
14.2o
18.3o
13.8o
15.7o
none of above is within 0.2o from the correct answer.
20. A 10.0–kg block is released from rest at point “A” in the figure below. The track is
frictionless except for the portion between points “B” and “C”, which has a length of
6.00 m. The block travels down the track, hits a spring of force constant 2 200 N/m,
and compresses the spring 0.45 m from its equilibrium position before coming to rest
momentarily. Determine the coefficient of kinetic friction between the block and the
rough surface between points “B” and “C”.
a.
b.
c.
d.
e.
0.07
0.12
0.25
0.33
none of above is within 10% from the correct answer.
21. In the previous setting, imagine the block will be going back and forth between the
slope and the spring before coming to a complete stop. How many times will it pass
point B (counting from when it is released from point A)? (hint: while you can, you
may not need to use the answer from the previous problem.)
a.
b.
c.
d.
e.
2
3
4
5
other