PHYSICS 51 MIDTERM EXAM - FALL 001 Name Student Number CHECK ONE: Smith 9:00 Ingram 10:00 Ingram/Hla :00 Note that problems 1-10 are worth points each, while problems 11-13 are worth 10 points. There is only one correct answer for each of questions 1-10. For answers with numerical values choose the closest to your answer. For questions 11-13, for full credit explain what you are doing, round your final answer to three significant figures and give the units. The last page of the exam has some equations and physical constants. PUT YOUR ANSWERS TO QUESTIONS 1-10 IN THE BOXES BELOW THIS LINE 1 6 7 3 8 4 9 5 10 PLEASE DO NOT WRITE BELOW THIS LINE total for 1-10 score for 11 score for 1 score for 13 total for exam 1
Please put the letter of the correct answer for each question in the numbered box on the first page. 1. Four successive displacements of 3 km, 4 km, 5 km, and 4 km are at right angles to each other as shown in the diagram. The magnitude of the resultant displacement is: A) km B) 16 km C) 3 km D) 5 km. The graph shows the velocity of a particle as a function of time. In the 1 s shown, the particle travels A) 0 m B) 100 m C) 640 m D) 440 m E) 00 m 3. A balloon is ascending at a rate of 5.0 m/s at a height of 9.6 m above the ground when a package is dropped. The time taken, in the absence of air resistance, for the package to reach the ground is: A) 1.0 s B) 1.5 s C).0 s D).5 s E) 3.0 s 4. Only one of the following statements is correct. The correct statement is A) Average velocity is not a vector quantity. B) The average velocity can always be expressed as one-half the sum of the initial and final velocities. C) An accelerating body always changes its direction of motion. D) The instantaneous velocity is equal to the time rate of change of the displacement. E) A body undergoing constant acceleration changes its velocity by larger increments in succeeding equal time intervals. 5. A car is traveling south at 30 km/h. It rounds a curve, and 6 s later it is traveling west at 30 km/h. The magnitude of the average acceleration of the car is: A) zero B) 60 km/has C) 5 km/has D)50 km/has E) 7.1 km/has
6. According to Newton's first law, the law of inertia, A) objects moving with an initial speed relative to a given frame of reference eventually come to rest relative to the reference frame. B) an object in an inertial reference frame remains at constant velocity or at rest unless acted upon by a net external force. C) rest is the most natural state of motion. D) an object at rest in a given frame of reference eventually finds itself in motion relative to the frame of reference. E) forces always exist in pairs. 7. A force F produces an acceleration a on an object of mass m. A force 3F is exerted on a second object, and an acceleration 8a results. What is the mass of the second object? A) 3m B) 9m C) 4m D) (3/8)m E) (8/3)m 8. The acceleration due to gravity on the moon is only about 1/6 of that on earth. An astronaut whose weight on earth is 600 N travels to the lunar surface. His mass as measured on the moon is A) 600 kg B) 100 kg C) 61. kg D) 10.0 kg E) 360 kg 9. An 80-kg man on ice skates pushes a 40-kg boy, also on skates, with a force of 100 N. The force exerted by the boy on the man is A) 00 N B) 100 N C) 50 N D) 40 N E) zero unless the boy pushes back. 10. When a particle moves in a circle with constant speed, its acceleration is A) constantly increasing. B) constant in direction. C) zero. D) constant in magnitude. E) constant in magnitude and direction. 3
ROUND ALL NUMERICAL ANSWERS TO 3 SIGNIFICANT FIGURES AND GIVE THE UNITS FOR FULL CREDIT EXPLAIN WHAT YOU ARE DOING Indicate your answer for EACH part clearly 11. A gun is fired at 0 o to the horizontal at the edge of a cliff 300 m above a flat plane where its target is located. If initial speed of the shell the gun fires is 50 m/s: a) what is the maximum height of the shell above its starting point? b) what is the horizontal distance to the target? c) how long is the shell in the air? Ignore air resistance. a) max. ht. = b) range = c) time of flight = 4
ROUND ALL NUMERICAL ANSWERS TO 3 SIGNIFICANT FIGURES AND GIVE THE UNITS FOR FULL CREDIT EXPLAIN WHAT YOU ARE DOING Indicate your answer for EACH part clearly 1. A 0-kg block, m1, with a pulley attached slides along a frictionless ledge. It is connected by a massless string to a 5-kg block, m, via the arrangement shown. Find the acceleration of each block and the tension in the connecting string. acceleration of m1 = acceleration of m = tension = 5
ROUND ALL NUMERICAL ANSWERS TO 3 SIGNIFICANT FIGURES AND GIVE THE UNITS FOR FULL CREDIT EXPLAIN WHAT YOU ARE DOING Indicate your answer for EACH part clearly 13. A block of mass.00 kg is at rest on an incline with variable angle. The distance from the block to the bottom end of the incline is 3.00 m. The coefficient of static friction between the incline and block is 0.7, while the coefficient of kinetic friction is 0.3. Calculate a) the maximum angle such that the block will not slide; b) if the incline is set to 40/, how long will it take the block to reach the bottom if it starts from rest; c) what is the speed of the block when it reaches the bottom? a) max angle = b) time c) speed = 6
v = vo + at x xo = vot + 1 at v = v + a( x x ) o o v+ vo x xo = t g = 981. m / s x = b ± b 4ac a a v r c = 7