Question

Driving in a car down Main Street, Tanner hit the breaks and accelerates at -5.2 m/s^2.

After 3.00 seconds he is moving at 20.0 m/s. What was his initial speed?

Answer 1

35.6 m/s

Step-by-step explanation:

This question can be solved using a kinematic equation, since there is a constant acceleration. First, let's define our given variables:

`a = -5.2 m/s^2\\t = 3.00 s\\V_f = 20.0 m/s`

To solve, we can use the equation:

`V_f = V_i + at`

Solved for initial velocity, this gives us:

`V_i = V_f - at`

Plugging in our given values, we can calculate the initial speed:

`V_i = 20.0 m/s - (-5.2 m/s^2)(3.00s)\\V_i = 35.6 m/s`

Note: this equation is solving for velocity, not speed. The speed of the car in this situation is simply the absolute value of the velocity. So in this case, the velocity is equal to the speed.