Question

A car is traveling at a speed of 70 mph, a long a straight road, when the driver slams on the brakes and the car m and the car a,=- 2.00 accelerates at comes to a complete stop. How much time passes between the time when the brakes were applied and the instant the car comes to a complete stop and how far did the car travel in that time? (1609 meters 1 mile, 3600 seconds 1 hour) a.) 7.28 s and 422.10 m. b.) 15.64 s and 244.70 m. c.) 12.32 s and 428.73 m. d.) 14.53 s and 210.98 m. e.) None of the above.

Answer 1

Answer:

Option B is the correct answer.

Explanation:

Speed of car = 70mph $=70\times \frac{1609}{3600}=31.28m/s$

Deceleration of car = 2 m/s²

We have equation of motion

          v = u + at

          0 = 31.28 - 2 t

           t = 15.64 seconds.

We also have

          $s=ut+\frac{1}{2}at^2=31.28\times 15.64-\frac{1}{2}\times 2\times 15.64^2=244.70m$

Option B is the correct answer.