PHYSICS 218 EXAM 1 Monday, September 24, 2007

Transcription

1 PHYSICS 218 EXAM 1 Monday, September 24, 2007 NAME: SECTION: Note: 525 Recitation Thurs 2: Recitation Tues 9: Recitation Thurs 3: Recitation Tues 12: Recitation Thurs 4: Recitation Tues 3: Recitation Thurs 5: Recitation Tues 6:55 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) A disoriented physics professor drives 4.25 km north, then 3.35 km west, and then 1.50 km south. Find the direction of the resultant displacement. Assume east defines the +x direction and north defines the +y direction. Direction 2. (5 points) In the fastest measured tennis serve, the ball left the racquet at m/s. Assume the served tennis ball was in contact with the racquet for 28.0 ms and started from rest. How far did the ball travel while it was in contact with the racquet? Distance 3. (5 points) A Ferris wheel with a radius of 13.0 m is starting up. A passenger on the rim of the wheel is moving in circular motion at 3.3 m/s, and is gaining speed at a rate of m/s 2. Find the magnitude of the passenger s acceleration at this moment. Acceleration

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) A river flows due south with a speed of 2.50 m/s. The river is 850 m wide. You are steering a motorboat that can move through the water at a speed of 4.25 m/s. You start from one bank, and want to reach a point on the opposite bank directly east of your starting point. (a) In what direction should you aim the motorboat? (b) How much time will be required to cross the river? Direction Time

4 5. (15 points) A hot-air balloonist, rising vertically with a constant velocity of magnitude 6.00 m/s, releases a sandbag at an instant when the balloon is 45.0 m above the ground. Take y = 0 to be on the ground, and neglect air friction. (a) What is the greatest height above the ground that the sandbag will reach? (b) How many seconds after its release will the bag strike the ground? (c) Sketch a y -t, v y -t, and y-t graphs on the axes provided. Be sure to label each graph clearly. Height a y Time v y y t t t

5 6. (15 points) The acceleration of a bus is given by a x (t) = (1.35 m/s 3 ) t. At t = 0, the velocity of the bus is 4.00 m/s and its position is x = 5.50 m. Find the velocity and position of the bus at t = 2.00 s. Velocity Position

6 7. (15 points) A ball is launched up a semicircular chute in such a way that at the top of the chute, just before it goes into free fall, the ball has a centripetal acceleration of magnitude 15.0 m/s 2. The radius of the chute is R = 35.0 cm. Neglect air friction. (a) How long is the ball in flight? (b) How far from the bottom of the chute does the ball land? (c) What is the speed of the ball at the instant before it strikes the ground? Time of flight Distance Speed