Download Physics 220 – Exam #1

Physics 220 – Exam #1
September 13
2000
This exam consists of 12 problems on 7 pages. Please check that you have them all.
All of the formulas that you will need are given below. You may also use a calculator.
sin θ = y/r
cos θ = x/r
tan θ = y/x
r
y
θ
x
average speed =
distance traveled
time
g = 9.8 m/s
2
1 mile = 1.6 km
average velocity = v =
displacement
time
instantaneous velocity = slope of position versus time
instantaneous acceleration = slope of velocity versus time
For constant acceleration:
x = x0 + v0 t + 12 at2
v = v0 + at
v 2 = v02 + 2a(x − x0 )
F = ma
Ffmax
riction = μS N (static friction)
Ff riction = μK N (sliding friction)
Fgravity =
1
Gm1 m2
r2
1. A golf ball is hit with an initial velocity of 75 m/s at an angle of 37◦ with respect to
the horizontal. How long does it spend in the air? Neglect the effects of spin and air
drag.
(a) 4.6 s
(b) 15.3 s
(c) 45 s
(d) 7.7 s
(e) 9.2 s
2. Two blocks are connected by a rope which runs over a pulley as shown in the figure.
Find the acceleration of the mass on the right. Ignore friction, and assume that the
masses of the rope and pulley are very small.
mm= =5.0
kg
5 kg
mm==3.0
3.0kg
kg
(a) 9.8 m/s2
(b) 3.7 m/s2
(c) 26 m/s2
(d) 6.1 m/s2
(e) 0.60 m/s2
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3. A hockey puck of mass 0.25 kg is sliding down an inclined plane as shown below. Find
the acceleration of the hockey puck. Ignore friction.
o
30
(a) 4.9 m/s2
(b) 2.2 m/s2
(c) 8.5 m/s2
(d) 9.8 m/s2
(e) 6.9 m/s2
4. You are trying to slide a refrigerator across a horizontal floor. If the mass of the
refrigerator is 200 kg and you need to exert a force of 300 N to make it just begin to
move, what is the coefficient of static friction between the floor and the refrigerator?
(a) 0.033
(b) 0.50
(c) 0.33
(d) 0.15
(e) 0.67
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5. What is the magnitude of the average acceleration of a skier who, starting from rest,
reaches a speed of 11 m/s after traveling down a slope for 4.0 s?
(a) 9.8 m/s2
(b) 2.8 m/s2
(c) 0.36 m/s2
(d) 1.5 m/s2
(e) 15 m/s2
6. The figure below shows the height as a function of time for a baseball which is thrown
from centerfield to homeplate. At which point on the graph is the velocity component
vy zero and the acceleration along y negative. The y direction is vertical, and the
“positive” direction is “up”.
y
B
C
A
D
t
(a) A
(b) B
(c) C
(d) D
(e) It never happens.
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7. A watermelon is dropped from the top of a building. If it takes 1.2 s for the watermelon
to reach the ground, how tall is the building? Ignore air drag.
(a) 14 m
(b) 4.9 m
(c) 25 m
(d) 7.1 m
(e) 9.8 m
8. Your car (m = 1200 kg) has a dead battery, and is initially at rest. You want to push
it so that it reaches a velocity of 1.5 m/s in 75 s. What is the force that you must
exert on the car? Ignore fricion. The road is horizontal.
(a) 24 N
(b) 0.020 N
(c) 9.8 N
(d) 12,000 N
(e) 48 N
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9. A horizontal rifle is fired at a target. The speed of the bullet as it leaves the rifle is
800 m/s. If the target is 50 m away, how far will the bullet fall vertically on its way to
the target?
(a) 0.31 m
(b) 9.8 m
(c) 0.019 m
(d) zero
(e) 0.038 m
10. A car of mass 1000 kg accelerates uniformly from rest, and reaches a speed of 15 m/s
after it has traveled 80 m. What is the magnitude of the acceleration?
(a) 1400 m/s2
(b) 0.094 m/s2
(c) 2.8 m/s2
(d) 9.8 m/s2
(e) 1.4 m/s2
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11. In class we did a demonstration involving two people on flat carts. One exerted a
force on one end of a rope while the other would just hang on. Which of the following
principles or ideas was this demonstration designed to illustrate?
(a) Newton’s second law: F = ma.
(b) Some motion can be frictionless.
(c) Newton’s third law: the action/reaction principle.
(d) All things are accelerated by gravity with the same acceleration.
(e) Ropes can apply a tension force.
12. A baseball of mass 0.40 kg is dropped from a tall bridge. The magnitude of air resistance that opposes its motion is 1.5 N. What is the magnitude of the acceleration of
the baseball?
(a) 9.8 m/s2
(b) 6.1 m/s2
(c) 0.60 m/s2
(d) 1.5 m/s2
(e) 3.8 m/s2
The End
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