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Unformatted text preview: kuruvila (lk5992) HW02 gokce (P111S11) 1 This printout should have 21 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points The velocity of the transverse waves produced by an earthquake is 6 . 78 km / s, while that of the longitudinal waves is 11 . 187 km / s. A seis mograph records the arrival of the transverse waves 71 . 9 s after that of the longitudinal waves. How far away was the earthquake? Correct answer: 1237 . 45 km. Explanation: Let : v t = 6 . 78 km / s , v = 11 . 187 km / s , and t = 71 . 9 s . If the distance to the earthquake is d , then the time lag is t = d v t d v = d ( v  v t ) v v t d = t v v t v  v t = (71 . 9 s) (11 . 187 km / s) (6 . 78 km / s) 6 . 78 km / s 11 . 187 km / s = 1237 . 45 km . Note: The longitudinal wave travels faster than the transverse waves. In fact, the ratio of the longitudinal velocity to the transverse wave velocity should be about 3 . 002 (part 1 of 2) 10.0 points A runner is jogging at a steady 7 . 3 km / hr. When the runner is 2 . 8 km from the finish line, a bird begins flying from the runner to the finish line at 14 . 6 km / hr (2 times as fast as the runner). When the bird reaches the finish line, it turns around and flies back to the runner. L v b v r finish line How far does the bird travel? Even though the bird is a dodo, assume that it occupies only one point in space (a zero length bird) and that it can turn without loss of speed. Correct answer: 3 . 73333 km. Explanation: Let : v r = 7 . 3 km / hr , L = 2 . 8 km , and v b = 2 v r . finish line L 1 dr 1 db 1 The runner travels a distance x until the encounter with the bird. In that time, the bird has traveled a distance L +( L x ) = 2 L x . The bird travel 2 times as fast as the runner during this time frame, so d b = 2 d r 2 L x = 2 x 2 L = 3 x x = 2 3 L and the bird flies a distance of d b = 2 L 2 3 L = 4 3 L = 4 3 (2 . 8 km) = 3 . 73333 km . 003 (part 2 of 2) 10.0 points After this first encounter, the bird then turns around and flies from the runner back to the finish line, turns around again and flies back kuruvila (lk5992) HW02 gokce (P111S11) 2 to the runner. The bird repeats the back and forth trips until the runner reaches the finish line. How far does the bird travel from the be ginning (including the distance traveled to the first encounter)? Correct answer: 5 . 6 km. Explanation: The distance remaining for the runner after the first encounter is L 1 = 1 3 L , and again the bird will fly 2 times as far as the runner until the next encounter. This pattern repeats over the entire original distance, so d b = 2 L = 2 (2 . 8 km) = 5 . 6 km ....
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This note was uploaded on 02/12/2011 for the course PHYS 111 taught by Professor Moro during the Spring '08 term at NJIT.
 Spring '08
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