PHYSICS 218 EXAM 1 Thursday, September 24, 2009

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1 PHYSICS 218 EXAM 1 Thursday, September 24, 2009 NAME: SECTION: Note: 525 Recitation Wed 9:10-10: Recitation Wed 11:30-12: Recitation Wed 1:50-2: Recitation Mon 11:30-12:20 There are a total of 7 problems on this test: Problems 1, 2, and 3 are worth 5 points each. For these three problems, points will be deducted for the wrong units or wrong number of significant digits. Other than that, no partial credit will be awarded for incorrect answers. Problems 4, 5, 6, and 7 are worth 15 points each. For these four problems, partial credit will be awarded where appropriate. For all 7 problems: You must show your work and/or explain your reasoning to receive any credit for a problem; merely stating the answer is NOT sufficient. Write your final answer(s) in the blanks provided. You may use the backs of the pages for scratch calculations if you wish, but only the work in the spaces provided on the front of the pages will be graded. For numerical values, assume that all specified digits are significant, including trailing zeros. Also remember, an answer CAN NOT be completely correct if it has the wrong units or the wrong number of significant digits. G O O D L U C K!!!!!

2 For problems 1, 2, and 3, do your work in the space provided, and write your final answer in the blank. Points will be deducted for the wrong units or wrong number of significant digits. Other than that, no partial credit will be awarded for incorrect answers. 1. (5 points) In the figure below, the vector A has a length of 11.0 m and the angle θ= Compute the x- and y-components of A. x-component y-component 2. (5 points) In a carnival ride, the passengers travel at a constant speed in a circle of radius 5.5 m. They make one complete circle in 4.0 s. What is their acceleration? Acceleration 3. (5 points) An automobile and a truck start from rest at the same instant, with the automobile initially some distance behind the truck. The truck has a constant acceleration of 2.20 m/s 2, and the automobile an acceleration of 3.50 m/s 2. The automobile overtakes the truck after the truck has moved 40.0 m. How far was the automobile behind the truck initially? Distance

3 For problems 4, 5, 6, and 7, do your work in the space provided, and write your final answer in the blank. For these problems, partial credit will be awarded where appropriate, based on the work that you show. 4. (15 points) Sam heaves a 16-lb shot straight upward, giving it a constant upward acceleration from rest of 42.0 m/s 2 for 60.0 cm. He releases it 2.20 m above the ground. You may ignore air resistance. (a) What is the speed of the shot when Sam releases it? (b) How high above the ground does it go? (c) How much time does he have to get out of its way before it returns to the height of the top of his head, 1.80 m above the ground? Speed Height Time

4 5. (15 points) A quarterback is set up to throw the football to a receiver who is running with a constant velocity v r directly away from the quarterback and is now a distance D away from the quarterback. The quarterback figures that the ball must be thrown at an angle θ to the horizontal and he estimates that the receiver must catch the ball a time interval t c after it is thrown to avoid having opposition players prevent the receiver from making the catch. In the following you may assume that the ball is thrown and caught at the same height above the level playing field. Assume that the y coordinate of the ball at the instant it is thrown or caught is y=0 and that the horizontal position of the quarterback is x=0. (a) Find v oy, the vertical component of the velocity of the ball when the quarterback releases it. (b) Find v ox, the horizontal component of the velocity of the ball when the quarterback releases it. v oy v ox

5 6. (15 points) An object s velocity is measured to be v x (t) = 3.0 m/s (2.5 m/s 3 )t 2. At t=0, the object is at x=0. (a) Calculate the object s position and acceleration as functions of time. (b) What is the object s maximum positive displacement from the origin? Position Acceleration Displacement

6 7. (15 points) A 124-kg balloon carrying a 22-kg basket is descending with a constant downward velocity of 20.0 m/s. A 1.0-kg stone is thrown from the basket with an initial velocity of 17.0 m/s perpendicular to the path of the descending balloon, as measured relative to a person at rest in the basket. The person in the basket sees the stone hit the ground 6.50 s after being thrown. Assume the balloon continues its downward descent with the same constant speed of 20.0 m/s. (a) How high was the basket when the stone was thrown out? (b) What is the horizontal displacement of the stone from the time it s thrown until it hits the ground? (c) Just before the rock hits the ground, find its horizontal and vertical velocity components, as measured by an observer (i) at rest in the basket and (ii) at rest on the ground. Height Displacement (i) Horizontal velocity (i) Vertical velocity (ii) Horizontal velocity (ii) Vertical velocity