Question

A race car is moving with a velocity of 144 kilometers/hour. The driver applies the brakes, and the car comes to a halt in 12.0 seconds. What is the acceleration of the car after 12.0 seconds?. a) -12.0 meters/second^2. b) -3.3 meters/second^2. c) 3.3 meters/second^2. d) 10.3 meters/second^2

Answer 1

To answer, first, convert the given velocity in km/h to m/s as shown below,
                        (144 km / hr) x (1000 m / 1 km) x (1 hr / 3600 s) = 40 m/s
The acceleration (a) is solved by through the equation,
                                     a = (Vf - Vi) / Δt
where Vf and Vi are final and initial velocities, respectively and Δt is change in time. Substituting the known values,
                                     a = (0 - 40 m/s) / 12 s = -3.3 m/s²
Thus, the answer to this item is letter B.

Answer 2

Velocity of the race car = 144 kilometers/hour
It needs to be converted to meters per second because the answer is in meters per second.
Then
Velocity of the race car = (144 km / hr) x (1000 m / 1 km) x (1 hr / 3600 s) meters/second
                                      = 40 meters/second
Initial velocity of the race car (V1) = 40 m/s
Final velocity of the race car (V2) = 0 m/s
Time taken by the car to come to a halt = 12 seconds
Acceleration of the car = (V2 - V1)/time
                                     = (0 - 40)/12
                                     = - 3.3 m/s^2
From the above deduction, we can conclude that the correct option among all the options that are given in the question is option "b".