GED Science TestPhysical ScienceMedium
A car traveling at 20 m/s applies its brakes and comes to a complete stop in 4 seconds. Assuming constant deceleration, what is the distance the car travels during this braking period?
- A40 meters
- B100 meters
- C20 meters
- D80 meters
Show answer & explanationAnswer & explanation
Correct answer: A. 40 meters
To find the distance, we can use the formula d = (vi + vf)/2 * t. The initial velocity (vi) is 20 m/s, the final velocity (vf) is 0 m/s, and the time (t) is 4 s. So, d = (20 m/s + 0 m/s)/2 * 4 s = (10 m/s) * 4 s = 40 meters.
Why the other options are wrong
- B. This is an incorrect calculation, possibly from squaring a number or using a wrong formula.
- C. This would be the distance if the car traveled at 5 m/s for 4 seconds, or if only initial velocity was considered without averaging.
- D. This would be the distance if the car maintained its initial speed for the entire 4 seconds (20*4).
Kinematic Equation (Distance with Avg. Velocity)
One of the kinematic equations used to calculate displacement (distance) when initial velocity, final velocity, and time are known, assuming constant acceleration.
- Formula: d = (vi + vf)/2 * t
- vi = initial velocity, vf = final velocity, t = time
- Applies to motion with constant acceleration (or deceleration)
Memory trick: Distance is the Average Speed's Time Travel.