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PHYSICS EOS FALL REVIEW 2014 KEY
Marcus, Christine, Mary, and John performed three experiments to calculate the coefficient of static friction
between a car tire and the street. Their results are listed in the table below. The tire’s actual coefficient of static
friction as calculated by the tire company is 0.77.
Marcus
Mary
Christine
1.01
0.78
0.70
1.03
0.71
0.85
0.99
0.83
0.99
1. Which one of the students had the most precise calculations?
Marcus is most precise b/c the RANGE of his numbers was the lowest at 0.04
John
0.79
0.83
0.73
2. Which one of the students had the most accurate calculations?
Mary, b/c her AVERAGE is 0.773, which is the closest to the accepted value of 0.77
3. In your own words describe the difference between accuracy and precision. DO NO say that one is
“more correct” or “more accurate” than the other, that would be incorrect.
Accuracy-the average of the numbers is the closest to the accepted value
Precision – the range of the numbers is the lowest
4. A runner is training for a marathon. During one of his training sessions he runs North for two hours and
covers a distance of 10 kilometers. He gets distracted by an ice cream stand and takes 15 minutes to
enjoy a cone. Once finished he decides to head home and takes 1.5 hours to run 5 kilometers South
where he stops at a Snuffer’s ending his training session with some cheese fries.
What was his average speed for the trip?
Speed = total distance
Total time
So Speed = 15,000 meters
12,420 seconds
distance = 10 km + 5km = 15 km, then convert to meters by multiplying by 1000
time = 2h + 15 min + 1.5 hr = 3hr, 45 min. convert to seconds; mult. by 3600
= 1.2m/s
5. Using the problem above, what was his displacement when he ended his training session?
5 km N, or 5,000 m N
6. Patrice swims due North across a river at 3 m/s. The river flows Due East at 3 m/s. What is her resultant
velocity? Hint: Make a diagram.
3m/s
3m/s
a2 + b2 = c2 so…
32 + 32 =c2
18 = c2
Ans: 4 m/s E of N
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7. Which of the following graphs above represents an object under constant acceleration? A
Which graph shows no acceleration acting on the object? B or D
Consider the graph below.
8. Determine the average speed for the following times.
0-2 sec
4-6 sec
6-10 sec
10 m = 5m/s
2s
0m = 0m/s
2s
20m
4s
=5m/s
10-12 sec
20m =10m/s
2s
9. What is the total distance traveled by the vehicle from 0 to 3 seconds?
6 meters
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Consider the graph below.
10. What is the total distance traveled by the object between second 2 and second 5?
Velocity or speed = distance so distance = velocity x time, so 30m/s x 3s = 90m/s2
time
11. When does the object have a constant velocity? How can you tell?
No, if it did, the graph would just be a flat line
12. When does the object have a positive acceleration? Between 1-2 seconds
What is the acceleration from time 1 to 2?
a=vf -vi so 30-0 = 15m/s2
Δt 2 What is the acceleration from time 6 to 9? 5-30 = -25 = 8 m/s2
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13. An apple falls 3m straight down from its tree. What is the final speed of the apple right before it hits the
ground?
vf2 = vi2 + 2ad
vi = 0
vf = FIND
Ans: 7.7 m/s
d=3
a = 9.8
t = NOT IN IT
14. A football player hits an opponent with a force of 150 Newtons. If the mass of the opponent is 100
kilograms and the opponent was not moving, find the acceleration of the player that was hit. Assume the
collision is perfectly elastic.
F=ma
150 N = 100a = 1.5 m/s2
100
100
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15. Given the free body diagram above which vector best represents the weight on the cart? 2
Normal force? 3
16. If arrow 1 represents the applied force then which arrow would represent the friction force?
Arrow 4
17. What is the mass of an object that weighs 196 Newtons?
FWEIGHT = mg so 196 N = m (9. 8) = 20 kg
9.8
9.8
18. There are two types of friction, static and kinetic, determine the difference between the two.
Static friction = nonmoving friction….this will increase until the object begins moving
Kinetic friction = amount of friction force AFTER object moves
19. From the graph below determine what the static friction is between the two objects.
Static friction =the maximum
Value of the data, so in this case
It it 1.2 N
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20. A cannon shoots a projectile along a parabolic path, see diagram, and encounters no air resistance. At point 2
what is the direction of the projectile’s acceleration, if any? What direction does the net force point?
The acceleration is always -9.8 m/s2 going downwards and the net force points exactly in the same direction: without
friction the only force is weight
21. Max and Mina are attempting to move their refrigerator out of their kitchen. Max and Mina are not the brightest
of movers, thus Mina is pushing the fridge to the North with a force of 62N and Max is pushing the fridge towards
the South with a force of 108N. What is the magnitude and direction of the net force on the refrigerator?
62 N
Ans: 46 N south
fridge
108 N
22. If the mass of the refrigerator is 300kg then how much acceleration do Max and Mina create on the refrigerator?
F = ma
Ans: 0.15 m/s2
23. The Earth travels in a circular motion around the Sun. What direction would its velocity vector be if the gravity
between the Earth and the Sun suddenly ceased to exist? BE SPECIFC! DO NOT SAY AWAY!
It will go off in a straight line tangent to the circle
24. On the figure above draw in the force acting on the object, the tangential velocity of the object and the
acceleration acting on the object. Not enough information to answer this question
25. From the figure above: Object 2 is orbiting object 1 currently at a distance of 1x108 meters. Object 1’s mass is
1x1020 kg and the mass of object two is 1x1010 kg. What is the force of gravity between them if the gravitational
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constant is still 6.67x10-11 N.m2/kg2 ? Ans: 6.67 x 10 N
26. Two objects attract each other with a force of gravity (Fgrav) of 36 N. If the distance separating the objects is
doubled and the masses one of the objects is tripled, then what is the new force of gravitational attraction?
G m1 m2
d2
36 =(1)(3)
2d2
= 36 = 3
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Ans: 27 N
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27. Two objects attract each other with a force of gravity (Fgrav) of 36 N. If the distance separating the objects is
increased by a factor of 4 and the masses of both objects are tripled, then what is the new force of gravitational
attraction?
G m1 m2
d2
36 =(3)(3)
4d2
= 36 = 3
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Ans: 20 N
28. A car accelerated from zero to 10 m/s in 5s. If the mass of the car is 1,000 kg, what was the average force required
to accelerate it to its final velocity?
1. a= 10 = 2 m/s2
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2. F = ma Ans: 2,000N