Phyus 111 Common Exam 1

Physics 111 Common Exam 2 March 8, 2002 Signature______

Name (Print) ______4 Digit ID______Section ______

Instructions: . You may use a 5x8 card or both sides of an 8.5 x 11 sheet for notes and as a formula sheet. . Questions 1 through 7 are worth 7 points each. Answer each question on the Scantron sheet. . Your name and section # must appear on the Scantron form also. . Questions 8 through 10 are worth 18 points each. You must show your work for these. . Please turn off any cell phones, pagers etc. . For all problems, g = 9.80 m/s2.

1. An object placed on an equal-arm balance requires 24 kg to balance it. When placed on a spring scale, the scale reads 24 kg also. Everything (balance, scale, set of masses and object) is now transported to the moon where free- fall acceleration is one-sixth that on Earth. The new readings of the balance and spring scale (respectively) are: A) 24 kg, 24 kg B) 4 kg, 4 kg C) 24 kg, 4 kg D) 4 kg, 24 kg E) 24 kg, 144 kg

2. A lead block is suspended from your hand by a string. The reaction to the force of gravity on the block is the force exerted by the: A) string on the block B) block on the string C) string on the hand D) hand on the string E) block on the Earth

3. A block is placed on an incline that has s = 0.5 and k = 0.4 and it does not slide down the plane. The maximum slope angle  is:

A) 51.30 B) 300 D) 23.50 E) 21.80

4. Circular highway entrance and exit ramps are often banked to accommodate cars traveling at 30 mph so that the cars do not have to rely on friction to make the turn. In order to similarly accommodate cars at 90 mph the planners should: A) Increase the radius by a factor of 3. B) Decrease the radius by a factor of 3. C) Increase the radius by a factor of 9. D) Decrease the radius by a factor of 9. E) Increase the radius by a factor of 1.71.

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5. A physics student weighing 640 N is standing on a spring scale (bathroom scale) in an elevator on the first floor. He can to go to the second floor (push 2) or to the basement (push B). As the elevator starts moving, the scale reads 800 N. Which button did he push and what is the magnitude of the elevator’s acceleration? A) 2 and 2.45 m/s2 B) B and 2.45 m/s2 C) 2 and 22 M/s2 D) B and 22 m/s2 E) 2 and 39.2 m/s2

6. A 0.50-kg object moves in a horizontal circular track with a radius of 2.5 m. An external force of 3.0 N, always tangent to the track, causes the object to speed up as it goes around. The work done by the external force as the mass makes one revolution is: A) 24 J B) 47 J C) 59 J D) 94 J E) 120 J

7. A block slides from rest down a frictionless ramp from a height h = 1 meter and hits a level surface whose coefficient

of kinetic friction k = 0.2. What distance d does it slide along the level surface before stopping? A) 0.2 m B) 0.5 m C) 2.0 m D) 5.0 m E) Need to know angle of the ramp

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8. Two blocks joined by a string passing over the usual massless pulley have begun to slide, starting from rest, on the 0 double inclined plane shown in the diagram. Both plane surfaces make 30 angles with the horizontal. Mass m1 is

100 kg and mass m2 is 50 kg. The coefficient of sliding friction k is 0.1 on both surfaces. a) Show on the sketch which way the system will accelerate and show which way the friction forces act. b) Draw the free body diagram and the Newton's Second Law equations for block 1. c) Do the same for block 2. d) Solve the equations for the acceleration of both blocks (make sure your answer agrees with your answer to part a).

M1 = 100 kg M2 = 50 kg

300 300

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9. The 4.0 kg mass in the figure is attached to a vertical rod by 2 strings. When the system rotates about the axis of the rod, the strings are under tension as shown and the tension T1 in the upper string is 70.0 N. a) Draw the free body diagram and write down the equations for the motion. b) Find the tension T2 in the lower cord. How many revolutions per minute does the system make?

1.25 m each

10. A student has proposed a design for an automobile crash barrier. When a 1200 kg car moving at 20 m/s crashes into it, a spring of negligible mass attached to the barrier slows the car to a stop. To avoid injuring the passengers, the maximum deceleration of the car as it slows cannot be greater than 5.0 g's (5 times the acceleration of gravity). a) Find the required spring constant k. b) Find the distance that the spring compresses in bringing the car to a stop. Ignore friction and energy lost by crumpling of the car. c) What happens after the car stops?