Question

#15 and #11

11. ssm A bicyclist makes a trip that consists of three parts, each in the same direction (due north) along a straight road. During the first part, she rides for 22 minutes at an average speed of 7.2 m/s. During the second part, she rides for 36 minutes at an average speed of 5.1 m/s. Finally, dur- ing the third part, she rides for 8.0 minutes at an average speed of 13 m/s. (a) How far has the bicyclist traveled during the entire trip? (b) What is her average velocity for the trip? 12. A car makes a trip due north for three-fourths of the time and due south one-fourth of the time. The average northward velocity has a magnitude of 27 m/s, and the average southward velocity has a magni- tude of 17 m/s. What is the average velocity (magnitude and direction) for the entire trip? 13. You are on a train that is traveling at 3.0 m/s along a level straight track. Very near and parallel to the track is a wall that slopes upward at a 12° angle with the horizontal. As you face the window (0.90 m high, 2.0 m wide) in your compartment, the train is moving to the left, as the drawing indicates. The top edge of the wall first appears at window cor- ner A and eventually disappears at window corner B. How much time passes between appearance and disappearance of the upper edge of the wall? 3.0 m/s 12° Problem 13 Section 2.3 Acceleration 14. Review Conceptual Example 6 as background for this problem. A car is traveling to the left, which is the negative direction. The direc- tion of travel remains the same throughout this problem. The car's ini tial speed is 27.0 m/s, and during a 5.0-s interval, it changes to a final speed of (a) 29.0 m/s and (b) 23.0 m/s. In each case, find the accelera- tion (magnitude and algebraic sign) and state whether or not the car is decelerating. 15. (a) Suppose that a NASCAR race car is moving to the right with a constant velocity of +82 m/s. What is the average acceleration of the car? (b) Twelve seconds later, the car is halfway around the track and traveling in the opposite direction with the same speed. What is the aver- age acceleration of the car?

Answer 1

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