PHY317K. Exam 1. February19, 2009 • Please, write your name clearly on top of th

Question

PHY317K. Exam 1. February19, 2009
• Please, write your name clearly on top of the page.
• You may use a formula sheet and a calculator. Cell phonesand laptops have to be on the
floor.
1. A soccer ball is kicked from the ground with an initial speed of19.5m/s at an upward angle
of 45o. A player 55m away in the direction of the kick startsrunning to meet the ball at that
instant.
(a) (10 points) How long is the ball in the air?

3.22 s

2.81 s

4.64 s

1.02 s
(b) (10 points) What must be his average speed if he is to meet theball just before it hits
the ground? Neglect air resistance.

13.8m/s

33.3m/s

5.76m/s

19.5m/s
1
2. In the US we measure fuel efficiency of our cars by citing thenumber of miles you can drive on
1 gallon of gas (miles/gallon=mpg). In Europe, the same informationis given by quoting how
many liters of gas it takes to go 100 kilometers (liter/100kilometers). ( 1 mile= 1.609×103 m,
1 gallon= 3. 78 liters)
(a) (10 points) My current car gets 21 miles/gallon in city travel.What number should I
give to my Spanish friend so that she can compare it to the mileageof her car?

11 liters/100km

10 liters/100km

15 liters/100km

25 liters/100 km
(b) (10 points) The car I drove in England last summer needed 6liters of gas to go 100
kilometers. How many miles/gallon did it get?

25 mpg

27 mpg

39 mpg

6 mpg
3. A vehicle starts from rest and accelerates at a rate of 2.0m/s2in a straight line until it reaches
a speed of 20m/s. The vehicle then slows at a constant rate of1.0m/s2 until it stops.
(a) (10 points) How much time elapses from start tostop?

10 s

20 s

30 s

25 s
(b) (10 points) How far does the vehicle travel from start tostop?

100m

300m

200m

273m
2
4. (20 points)The coefficient of static friction between Teflon andscrambled eggs is about 0.04.
What is the smallest angle from the horizontal that will cause theeggs to slide across the
bottom of a Teflon-coated skillet?
3
5. (20 points) In the figure a car is driven at constant speed overa circular hill and then into
a circular valley with the same radius. At the top of the hill, thenormal force on the driver
from the car seat is 0. The driver’s mass is 70.0 kg. What isthe magnitude of the normal
force on the driver from the seat when the car passes through thebottom of the valley?
4

Explanation / Answer

initial speed v = 19.5 m/s
angle = 45° So, range R = v 2 sin 2 / g                     =38.8 m 1 (a) :     Time taken to reach the ground T = 2vsin / g                                                     =2.8139 s 1 (b) : 1 (b) :      So, distance moved by player S= 55 m - 38.8 m                                                          = 16.2 m       time taken to move thisdistance t = 2.8139 s       So,  average speed ofthe player   V = S / t                                                              = 5.75 m / s

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