1. Physics 218: Mechanics Instructor: Dr. Tatiana Erukhimova Lecture 4

2. A “police car” problem (cont.) x=0 x1x1 x2x2 V 3 =20m/s a=0 a p =kt x 2 – x 1 = 3.5 km V 1 =30m/sV 2 =40m/s You start moving from rest with constant acceleration. There is a police car hiding behind the tree. The policeman has a metric radar. He measures your velocity to be 30 m/s. While the policeman is converting m/s to mph, you continue accelerating. You meet another police car. This policeman measures your velocity to be 40 m/s. You also notice the police, drop your velocity to 20 m/s and start moving with a constant velocity. However, it is too late. This police car starts chasing you with acceleration kt (k is a constant). After some distance he catches you. a=const V(t=0)=0

3. A “police car” problem x=0 x1x1 x2x2 V 3 =20m/s a=0 a p =kt x 2 – x 1 = 3.5 km V 1 =30m/sV 2 =40m/s 1. What was your acceleration before you meet the second police car? 2. How long did you travel from x 1 to x 2 ? 3. Find x 1 4. At which distance does the police car catch you? 5.Convert the velocity from m/s to mph a=const V(t=0)=0

4. Have a great day! Reading: Chapter 2