A police officer is driving due north at a constant speed of 27 m/s relative to
ID: 2001486 • Letter: A
Question
A police officer is driving due north at a constant speed of 27 m/s relative to the ground when she notices a truck on the east-west highway ahead of her, driving west at a high speed. She finds that the truck's speed relative to her car is 55 m/s (about 120 mph). (a) Sketch the vector triangle that shows how the truck's velocity relative to the ground is related to the police car's velocity relative to the ground and to the truck's velocity relative to the police car. The sketch need not to be to scale, but the velocity vectors should be oriented correctly and bear the appropriate labels. This answer has not been graded yet. NOTE: Complete part (a) and then check your solution against the key after the assignment is due. Although this will not count directly for or against your score for this homework assignment, it is good preparation for the test. (b) What is the truck's speed, relative to the ground? m/s
Explanation / Answer
Velocity of the police with respectto ground VPE= 27j (due north)
Velocity of the truck with respectto police VTP= -55i (due west)
Velocity of the police with respect to ground VTE=VTP-VPE
= -55i- 27j (due SW)