Midterm α, Physics 1P21/1P91

Transcription

1 Midterm α, Physics 1P21/1P91 Prof. D. Crandles March 1, 2013 Last Name First Name Student ID Circle your course number above No examination aids other than those specified on this examination script are permitted (FHB A). Use or possession of unauthorized materials will automatically result in the award of a zero grade for this examination. This is a closed book test, only calculators are allowed Formulas not on the supplied formula sheet must be derived Attempt all questions Question Mark Out of 1 a b c d e 1 2 a b c d e 1 3 a b c d e 1 4 a b c d e 1 5 a b c d e Total 20 This exam contains 7 pages as well as an equation sheet. Please, verify that your copy is complete. 1

2 Physics 1P21/1P91 Midterm α, March 1, 2013 page 2 For questions 1 5: circle the correct answer on the front page. (1) 1. An object moving along a straight line is decelerating. Which one of the following statements concerning the object s acceleration is necessarily true? (a) The value of the acceleration is positive. (b) The direction of the acceleration is in the same direction as the displacement. (c) An object that is decelerating has a negative acceleration. (d) The direction of the acceleration is in the direction opposite to that of the velocity. (1) 2. A 1.44 kg book is sitting on a stationary table. What is the magnitude and direction of the force exerted on the table by the book. (a) 14.1 N up (b) 14.1 N down (c) 15.2 N up (d) 15.2 N down (2) 3. A force P (magnitude 160 N) pulls on a crate of mass m on a rough surface. The figure shows the magnitudes and directions of the forces that act on the crate in this situation. W represents the weight of the crate. FN represents the normal force on the crate, and f represents the frictional force. Which statement best describes the motion of the crate? (a) The crate must be at rest. (b) The crate must be moving with constant velocity. (c) The crate may be either at rest or moving with constant velocity. (d) The crate may be either at rest or moving with constant acceleration.

3 Physics 1P21/1P91 Midterm α, March 1, 2013 page 3 (1) 4. A baseball is hit upward and travels along a parabolic arc before it strikes the ground. Which one of the following statements is necessarily true? (a) The acceleration of the ball decreases as the ball moves upward. (b) The velocity of the ball is zero when the ball is at the highest point in the arc. (c) The acceleration of the ball is 0 m/s 2 when the ball is at the highest point in the arc. (d) The x-component of the velocity of the ball is the same throughout the ball s flight. (1) 5. An object is thrown straight downward from a high cliff with a speed that is LESS than the terminal velocity. Which of the following statements is necessarily true? (a) Initially, the drag force is greater than the gravitational force and the object slows down. (b) Initially, the drag force is less than the gravitational force and the object speeds up. (c) The drag force is constant like the kinetic frictional force. (d) Initially, the drag force is less than the gravitational force and the object slows down.

4 Physics 1P21/1P91 Midterm α, March 1, 2013 page 4 (5) 6. The graph below shows position versus clock reading histories for two trains moving along parallel tracks. (a) Mark with the symbol t a along the t-axis on the diagram any instant or instants when the trains are passing the other. (b) Which train, A or B, is moving faster at clock reading t b? (c) Mark with the symbol t c along the t-axis on the diagram any instant or instants at which the two trains have the same velocity. (d) Over the period of time shown in the graph, train B is i. speeding up all the time ii. slowing down all the time iii. speeding up part of the time and slowing down part of the time (CIRCLE THE CORRECT STATEMENT)

5 Physics 1P21/1P91 Midterm α, March 1, 2013 page 5 (5) 7. The following picture shows the position vector ( r) of a car of mass 750 kg which is moving in a circle of radius 90m at a constant speed of 10 m/s. The car is moving clockwise. The coefficients of friction are µ s = 0.25 and µ k = (a) Indicate the direction of the velocity vector in the picture above when the car is at position r. (b) Calculate the velocity of the car in unit vector notation when the car is at position r. (c) Show alloftheforcesactingonthecarinafreebodydiagramwhere gravityisdownward. (d) Determine the magnitude of the frictional force acting on the car. Is it static or kinetic friction? Explain.

6 Physics 1P21/1P91 Midterm α, March 1, 2013 page 6 (5) 8. A student standing on the ground throws a ball straight up. The ball leaves the student s hand with a speed of 15 m/s when the hand is 1.0 m above the ground. How long is the ball in the air before it hits the ground? (The student moves her hand out of the way.)