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, decelerating at a rate of 5 m/s². How long does it take for the car to come to a complete stop?
- A5 seconds
- B4 seconds
- C3 seconds
- D2 seconds
Show answer & explanationAnswer & explanation
Correct answer: A. 5 seconds
Using the kinematic equation v_f = v_i + at, where v_f = 0 m/s, v_i = 25 m/s, and a = -5 m/s², we solve for t: 0 = 25 + (-5)t, which gives 5t = 25, so t = 5 seconds.
Why the other options are wrong
- B. Incorrect calculation.
- C. Incorrect calculation.
- D. Incorrect calculation; 25/5 is 5, not 2.
Kinematic Equation (Time)
One of the equations of motion used to describe the relationship between initial velocity, final velocity, acceleration, and time for objects moving with constant acceleration.
- Equation: v_f = v_i + at
- v_f = final velocity
- v_i = initial velocity
- a = acceleration
- t = time
Memory trick: Speed changes with time, acceleration is the key.