You have a friend who just bought a new car. He wants to show you how fast it ca

Question

You have a friend who just bought a new car. He wants to show you how fast it can accelerate, so he takes you and the car to a local drag strip. (A drag strip is a race track that is short, straight and flat.) He asks you to measure the time that it takes him to travel from one end of the drag strip to the other, beginning from a standing start. You plan to use the stop watch on your smart phone to measure his time.

At the moment he starts his run, however, you realize that you have left your phone in his car. Since you are taking PHS101, however, this is not a problem. After the race, he tells you that his final speed was 94 miles per hour

The accelerometer on your smart phone says that his average acceleration was 0.002 miles / second2

How long did it take him to run his race? Your answer should be accurate to the nearest 0.1 second. Hints: Convert the final speed to miles per second before doing your calculation. You do not need to know the length of the drag strip to calculate the answer.

Explanation / Answer

Given

the final speed of the car is v = 94 mph = 0.0261111111111 miles/s

and the acceleration is a = 0.002 miles/s2

using equations of motion v = u+at

v = at , u initial velocity is zero

t = v/a = 0.0261111111111/0.002 s = 13.0556 s

so the time taken is t = 13.0556 s

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