EF 151 Exam #2 - Fall, 2014
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Name:
Section: _____________
Instructions:
 Put your name and section on the exam.
 Do not open the test until you are told to do so.
 Write your final answer in the box provided
 If you finish with less than 5 minutes remaining, please stay seated until the exam is over.
 Stop work immediately when time is over; pass exams to the aisle; stay seated until all
exams are collected. Working after time is over results in an automatic 10 point deduction.
 Turn in your equation sheet with your examination
Guidelines:

Assume 3 significant figures for all given numbers unless otherwise stated

Show all of your work – no work, no credit

Include units for all answers and directions for all vectors
8:10
9.40
11:10
12:40
2:10
3:40
111
Front
S1aB
Daniel
S2a
Daniel
S3a
Tyler
S4a
Daniel
S5a
Tyler
S6a
Tyler
a
111
C
Back
S1b
Andrew
c
S2b
Andrew
S3b
Andrew
S4b
Brandi
S5b
Brandi
S6b
Brandi
bEst
209
S1c
A
Rachel
S2c
Rachel
S3c
Rachel
S4c
Jason
S5c
Jason
S6c
Jason
Est
201
S1d
Tayler
S2d
Tayler
S3d
Tayler
S4d
Sarah
S5d
Sarah
S6d
Sarah
EF 151 Exam #2 - Fall, 2014
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1. (2 pts) A baseball is rolled off a 3 ft high table. Just as the ball rolls off the table, a second baseball
is dropped from the same height. Which baseball hits the ground first? Neglect air resistance.
A. the baseball rolled off the table
B. the baseball that was dropped
C. both hit at the same time
D. cannot determine which hits first
2. (2 pts) Timothy kicks a soccer ball at 20 m/s at an angle of 35° above the ground. The minimum
speed while the ball is in the air is:
A. 0
B. 20cos(35°) m/s
C. 20sin(35°) m/s
D. 20tan(35°) m/s
E. 20 m/s
3. (2 pts) Tayler is walking at a velocity of +6 ft/s on a moving sidewalk that is going at +2 ft/s. Rachel
is walking alongside the sidewalk at a velocity of +5 ft/s. The velocity of Rachel with respect to Tayler
is:
A. -3 ft/s
B. -1 ft/s
C. +1 ft/s
D. +3 ft/s
4. (2 pts) Andrew has an acceleration with respect to the ground of (4i + 6j)ft/s2. Daniel has an
acceleration with respect to the ground of (3i – 2j)ft/s2. The acceleration of Daniel with respect to
Andrew is:
A. (1i + 8j)ft/s2
B. (-1i – 8j)ft/s2
C. (7i + 4j)ft/s2
D. (-32.2j)ft/s2
5. (2 pts) A cart is being pushed as shown. Neglect friction and air
resistance. The acceleration of the cart is:
A. 0.5 ft/s2
B. 2.0 ft/s2
C. 16.1 ft/s2
D. 64.4 ft/s2
6 lb
12 lb
EF 151 Exam #2 - Fall, 2014
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6. (2 pts) The correct FBD for a person sitting in a car that is moving to the left and slowing down is:
A
B
C
D
E
F
7. (2 pts) The static coefficient of friction between two objects is 0.8. Which value is not possible for the
coefficient of kinetic friction between the two objects?
A. 0.3
B. 0.5
C. 0.7
D. 0.9
8. (2 pts) What is the friction force between the box and the ground?
A. 12 lb
B. 18 lb
C. 20 lb
D. 30 lb
20 lb
30 lb
μs = 0.6, μk = 0.4
9. (2 pts) The terminal velocity of an object of mass M is V. What would the terminal velocity of an
object of mass 2M be? (same size and shape)
A. 2𝑉
B. √2𝑉
C. 𝑉
1
D.
𝑉
E.
√2
1
2
𝑉
10. (2 pts) Donnie Tyndall throws a basketball straight down. Considering air resistance, the
acceleration of the basketball the instant after release is:
A. greater than gravity
B. equal to gravity
C. less than gravity
D. cannot determine
EF 151 Exam #2 - Fall, 2014
11. (16 pts) A water balloon is thrown out a window with an unknown
speed at the angle shown. The balloon hits the ground 0.6 seconds
after being thrown. How high is the window above the ground?
(assume ideal projectile motion)
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15°
y
v
Hits ground
0.6 seconds
after release
21 ft
12. (16 pts) Professor Schleter is driving his 20 kN minivan down a 1.4 degree incline. The drive
(traction) force is 1200 N and there is significant air resistance. Determine the instantaneous
acceleration when the van is traveling at 22 m/s. (FBD=KD required)
𝐹𝐷 = 12𝜌𝐴𝐶𝐷 𝑣 2
A = 2.9 m2
ρ = 1.2 kg/m3
Cd = 0.35
EF 151 Exam #2 - Fall, 2014
13. (16 pts) Two 3000 lb tractors are working together
to move a 2000 lb crate. The traction force of
each tractor is 1200 lb to the right. The crate is
Tractor
sliding and experiences a friction force of 1400 lb.
Determine the force in the connection (coupling)
between tractor A and the crate. (2 FBD = KD required)
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B
Crate
Tractor A
14. (16 pts) An airplane is flying at a speed of 250 mph 30° E of N with respect to the ground and 230
mph 22.7° E of N with respect to the air. What is the speed of the wind?
EF 151 Exam #2 - Fall, 2014
15. (16 pts) Brandi is pushing on a box with a force of 30 lbs.
What is the minimum force P that Sarah needs to pull on the
box to get it to move? (FBD required)
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P
30 lb
20°
120 lb
µs = 0.70, µk = 0.50