PHYS-1100 Fall 2010 Exam 3 answer key

PHYS-1100 Fall 2010 Exam 3 answer key - '1. According to...

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Unformatted text preview: '1. According to Newton's Second Law, a) objects which are at rest will remain at rest # b) acceleration magnitude is inversely proportional to inertia c) only stationary objects can accelerate d) forces come in pairs e) none of the above are consequences of the Second Law _9 ‘ c9 5' wrasp/uolbfi £9. [owe a : 1! iv mew/24(Mé55/ 7V? 2. Exactly three forces, all lying in the xy plane, act continuously on an object of mass, M. One force is in the direction of the —y axis, and a second force is of equal magnitude as the first and is in the direction of the —x axis. The object continues to move with a constant velocity whose vector direction lies in quadrant IV. in which quadrant must the third force vector (of unknown magnitude) lie? # a) quadrant 1 y b) quadrant 11 H c) quadrant 1H d) quadrant IV e) not enough information is provided. III iv ":3 19 _ V I; Q :0.) S‘jflgf’ M937! 56 0 . ‘9 ‘- f’7 d H a -0 W,K_/npivmm/3LJQCQ .1 3. What average force must be exerted in order accelerate a drag racing automobile from rest to 530 kin/hr (147 m/s) within the length of the quarter mile (400 m) track. The weight of the vehicle is 2250 pounds (1 X104 N) a) 1.0 x 104 N b) 7.2 x 104 N c) 2.8 >< 10% N d) 9.8 X 103 N e) none of the above are even approximately correct at: 4. A fisherman is towing his boat trailer with a pickup truck. To accelerate the truck and trailer away from a traffic signai the truck must exert a force of 1200 newtons on the trailer via the trailer hitch. How much force does the trailer exert back on the truck through the hitch? # a) just 1200 N if / b) somewhat less than 1200 N 3 my c) somewhat more than 1200 N r d) can‘t determine that force without knowing the acceleration 5. A 12 kg crate is initially at rest on a frictionless, 19 degree inclined ramp. A constant force of magnitude 100N, parallel to the plane and directed upwards along the plane, is exerted on the crate. Compared to the weight of the crate, is the magnitude of the normal component of the force exerted on the crate by the ramp greater than, less than, or equal to, the weight of the crate a) greater than the weight of the crate # 13) less than the weight of the crate 0) equal to the weight of the crate d) yes 6. If friction were to be introduced between the crate and the ramp in the previous question (5) with the crate still initially at rest, and with the 100 N force still acting, in what direction should the frictional force component be drawn on a free body diagram of the crate? a) parallel to the ramp, but in the “up the ramp" direction # b) parallel to the ramp, but in the "down the ramp” direction c) perpendicular to the ramp d) there will not be any frictional force component acting e) not enough information is provided our/Agra, fiat/I'm} 4507/ wan/d MWf 2P Adah/9 7. A 55.0 kg gymnast is climbing up a vertical rope that is attached to the gym ceiling. She is accelerating towards the ceiling at a rate of 0.75 rn/sg. What is the magnitude of the tension in the rope between her and the ceiling. You may neglect the mass of the rope, and, of course, any air resistance. # a) 580 N b) 500 N c) 480 N d) 540 N 6) none of the above are even approximately correct 8. The coefficient of static friction between automobile tires and concrete pavement is about 0.45 under wet conditions. What’s the steepest hill along which you can park your car without risking it sliding down the hill? 3) a slope of about 18 degrees from horizontal # b) a lepe of about 24 degrees from horizontal c) a slope of about 31 degrees from horizontal d) a slope of about 39 degrees from horizontal e) none of the above are even approximately correct 9. Which of the following is the most appropriate free body diagram to use in solving the previous problem . __ __ e) none of ' ' C ' '- " d these 7% 1.5 fall/{(417135 0%!) fun) 0%}ch cared” 7007(9'“ 9040/ 7’1113 {Mp/15:5 ‘ 3 charts (axis—#5“ five l0. In the figure above, all six blocks are of identical weight, all the ropes and pulleys are all massless, and the pulleys are frictionless. The level surface in "C" is also frictionless. Evaluate the tension in each string marked with "*” and decide in which case or cases is that tension equal in magnitude to the weight of a single block. a) case (A) only A + b) cases (13) and (C) only c) cases (A) and (B) only d) cases (A) and (C) only # e) all three cases (A) (B) and (C) C 'Frictionless surface 11. In the contraption pictured at right the strings can be considered to be massless, and the pulley to be both I I ' '- I ' massless and frictionless. The system is remaining in a state of rest in the situation pictured. What is the approximate tension in the section of string that is connected to the ceiling? a) 98 N b) 130 N c) 150 N # d) 180 N e) none of the above are even approximately correct 12. F ailing through air, a PingPong® ball will eventually reach a terminal velocity of about 9 m/s. Recall that the ball is subject to a drag force (air resistance) of magnitude fDII/2[CDpAv2}. If a hole were punched in the same ball and lead shot were poured inside until the mass of the ball was 16 times greater than it was when empty, the new terminal velocity would be about a) 144 m/s b)98m/s 7p a c)56m/s 07’ V7" p r m # d)36m/s c) 18 m/s [.4 M02 :3 my 2 2. fkg/w V; I: V} 13. A roller blade skater rounding a level (unbanked) curve senses the onset of a skid when his speed about 8.0 m/s. He knows that the coefficient of static friction between his wheels and the dry pavement is about 0.64 and from those facts he deduces the radius of the curve. The radius must be about # a)10 m b)5m c)20m d)15m e) none of these are even approximately correct '14. There is static and kinetic friction between the 75 kg box and the level floor pictured. The force, F, is applied at an angle with respect to the horizontal of 30 degrees and its magnitude is slowly increased. When the magnitude of F reaches 300 N, the box begins to slide across the floor. The coefficient of static friction between the box and the floor is approximately a) 0.18 (dimensionless) ' F b) 0.23 (dimensionless) ' e) 0.29 (dimensionless) d) 0.34 (dimensionless) e) none of the above are even approximately correct 15. If, after the box was started off as described in the previous question, the force, F, is maintained at the same 300 N magnitude as found above, a) the block would gradually slow down and stop b) the block would continue to slide at a steady speed c) the block would steadily increase in speed d) the block would experience a series of stops and starts 16. Which one of the acceleration vs time graphs below most appropriately represents the acceleration of an object that was released from rest, then falls freely through air, but is subject to the effect of air drag? Take the positive direction as being “towards the center of the Earth." (ii/\Q/ (ii a. t/ L 5 £12? Vii-7,9 l9 " 5u€57lrbh _— if H m t {J9 F 5 pr; 3 a la 5: (‘5 gut? rm g 17. When an automobile is roundng a banked highway curve at a speed that is almost, but not quite, too fast for the curve, which forces, or components of forces, form all or part of the required centripetalforce that keeps the car from skidding? a) the gravitational force b) the normal component of force c) the frictional component of force # d) both the normal and the frictional components e) both the frictional component and the gravitational force ...
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PHYS-1100 Fall 2010 Exam 3 answer key - '1. According to...

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