GED Science TestPhysical ScienceMedium
A car is traveling at a constant speed of 25 m/s. The driver sees an obstacle and applies the brakes, causing the car to decelerate at a constant rate of 5 m/s². How long does it take for the car to come to a complete stop?
- A5 seconds
- B2 seconds
- C10 seconds
- D125 seconds
Show answer & explanationAnswer & explanation
Correct answer: A. 5 seconds
To find the time, use the kinematic equation v_f = v_i + at. Here, v_f = 0 m/s (stops), v_i = 25 m/s, and a = -5 m/s² (deceleration). So, 0 = 25 + (-5)t, which gives 5t = 25, or t = 5 seconds.
Why the other options are wrong
- B. Incorrect calculation; perhaps 25/10.
- C. Incorrect calculation; perhaps double the correct answer.
- D. Incorrect calculation; possibly 25*5.
Kinematic Equation (Time)
One of the equations of motion used to describe the motion of objects with constant acceleration, specifically to find time.
- v_f = v_i + at (final velocity = initial velocity + acceleration × time).
- Can be rearranged to solve for time: t = (v_f - v_i) / a.
- Requires constant acceleration.
Memory trick: VAT and SAD are your kinematic pals.