1010, Fall 2003, Exam 1
GREEN:
ANSWERS ARE BOLDED
Write your name and ID on both your exam and your scantron answer sheet.
Write the color of your exam paper on the top of your scantron sheet next to your name.
Be sure to turn your exam in to the proper box.
Return
both the answer sheet and the exam.
This
test is closed book, but you may use a single 3x5 card with your own notes
written on it. You may also use a
calculator. The exam is worth 30
pts total.
For all of these problems, assume that air resistance is not important unless you are told otherwise.
Conversions you may or may not need:
1 pound = 4.45 N, 1 slug = 14.594 kg, 1 mph = 0.447 m/s.
Multiple
Choice and True/False Questions: 16 pts total
1. (1 pt) You weigh 140 lbs and you want to find out far a strong spring will stretch if you hang from it. So you first hook a 15 lb weight to it and you find it stretches by 0.03 m. How much will it stretch if you take off the weight and then hang from it yourself?
a. 0.28 m; b. 0.523 m; c. 0.093 cm; d. 0.47 m
2. (1 pt) I am riding my bicycle at 10 m/s while talking on my cell phone, and I run into a truck. My head, which has a mass of 5 kg, hits the wall of the truck and stops in 0.01 seconds. What is the average force on my head during the crash?
a. -500 N b. -5000 N c. -50 N d. -5 N e. -0.1 N
3. (1 pt) Being a slow learner, the next day I do the same thing, except this time I have put on a helmet and am riding faster, at a speed of 15 m/s. The cushioning on the helmet takes time to squash and so this time my head takes 0.05 seconds to stop. Under these circumstances, the magnitude (absolute value) of the average force on my head is:
A) greater than the magnitude of the average force on my head in the previous problem
C) equal to the magnitude of the average force on my head in the previous problem
D) to figure this out requires more information than what is given.
4. (1 pt) Having given up on bicycling, I am driving my car along a cliff 100 m above a river. While talking on my cell phone, I get distracted and drive over the edge of the cliff. I quickly open the door as the car is falling and push myself out of the car. I will hit the water
a. about 1 second after the car does; b. at about the same time as the car;
c. before the car; d. It is impossible to predict without knowing the masses of me and the car and how quickly I get out of the car.
5. (1 pt) What is the gravitational force in kg on a 20-pound block of wood?
a.
2.04 kg; b. 9.1
kg; c. 89.1 kg;
d. none of the above, because it is a trick question: kg is not a unit of
force.
Questions
6 – 7. A salesman sells peanuts by the pound using a spring scale that is very
well calibrated, reading 1 lb when 1 lb of peanuts is placed on the scale.
The spring in his scale broke one day when some place a lead brick on the
scale. He finds a replacement
spring that is identical in all respects except that it has a slightly higher
spring constant.
6. (1 pt) When he replaces the original spring and places 1 lb of peanuts on the scale,
a. the scale will read more than 1 lb.
b. the scale will read 1 lb.
c.
the scale will read less than 1 lb.
7. (1 pt) True (a) or False (b) When he places 1 lb of peanuts on the scale, the new spring will exert a larger force up on the peanuts than the original spring exerted on 1 lb of peanuts..
8. (1 pt) You drop a very dense 0.5 m diameter spherical rock off a 2000 m cliff. It is starting with a speed of 0 m/s and it falls for 7 seconds. During which second of the first five seconds it falls does the rock’s speed increase the most?
a. first second; b. third second; c. fifth (last) second; d. none of the above are correct because its speed increases by the same amount during each of the three intervals listed.
Questions 9 – 13. A person on a bicycle is coasting down a hill of constant slope.
9. (1pt) True (a) or False (b) Their velocity is constant.
10. (1 pt) True (a) or False (b) Their acceleration is constant.
11. (1 pt) True (a) or False (b) The net force on the person is constant.
12. (1 pt) True (a) or False (b) Their velocity is changing due to a gravitational force.
13. (1 pt) True (a) or False (b) If they are on earth, their acceleration will always be 9.8 m/s2.
14. (1 pt) A car is going 2 m/s and then accelerates for 13 seconds with an acceleration of 8 m/s2. After the 13 seconds it is going how fast?
a. 1354 m/s, b. 106 m/s, c. 10 m/s, d. 8 m/s, e. none of the above.
15. (1 pts) If a red 1979 car with a mass of 1200 kg is pushed with a net force of 325 Newtons on a day when the temperature is 85 degrees, how fast will it be moving 30 seconds after starting from rest? (The car is not moving before being pushed.)
A) 40.0 m/s; B) 40.0 mph; C) 8.1 m/s; D) 16.2 m/s; E) 10.8 m/s
16. (1 pt) An elevator, which together with its occupants has a mass of 1000 kg, is on its way from the 1st to the 100th floor and is traveling upwards at a constant speed of 10 m/s. If we define up to be the positive direction, the net force on the elevator
a. is +9.8 m/s2 b. is positive, but not 9.8 m/s2 c. is negative d. is zero
e. changes as it rises.