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**Problem 1:**

You drive at a constant speed of 20 miles/h around a city block, checking out the neighborhood. Are you accelerating?

- Answer:

Yes, the direction of the velocity vector is changing all the time.

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**Problem 2:**

You are traveling east at 30 miles per hour. You see a ball rolling onto the road and you break hard, because you are afraid that a child will come running after the ball. You come to a stop in 0.8 seconds. What is the direction of your average velocity in this short time interval? What is your average acceleration?

- Answer:

The direction of your average velocity is east. You are traveling east with decreasing speed until you come to a stop. The change in your velocity is D**v **= **v**_{2}-**v**_{1 }= 0 - 30 mph east = -30 mph east = 30 mph west. Let us convert to SI units.

30 mph times 1609 m/mile times 1 h/(3600 s) = 13.4 m/s.

Your average acceleration is D**v**/Dt = (13.4 m/s)/(0.8 s) west = 16.8 m/s^{2} west.