# This question is typical on some driver’s license exams:?

A car moving at 44 km/h skids

12 m with locked brakes.

How far will the car skid with locked brakes

at 110 km/h? Assume that energy loss is due

only to sliding friction.

Answer in units of m

### 3 Answers

- electron1Lv 74 weeks agoFavorite Answer
The constant is the deceleration of the car. I suggest that you use the following equation to calculate the acceleration.

vf^2 = vi^2 + 2 * a * d

The first step is to convert the velocity from km/h to m/s.

1 km = 1,000 m

1 h = 3,600 s

1km/h = 1000/3600 = 5/18

v1 = 44 * 5/18 =220/18

v2 = 110 * 5/18 = 550/18

0 = (220)^2 = 2 * a * 12

a = -(220/18)^2 ÷ 24

The acceleration is approximately -6.22 m/s^2

0 = (550/18)^2 + 2 * -[(220/18)^2 ÷ 24] * d

d = (550/18)^2 ÷ -[(220/18)^2] * 2 = 75 meters

Now let me show you a much easier way to solve this problem. According to the following equation, the distance the skids is directly proportional to the square of the initial velocity.

vf^2 = vi^2 + 2 * a * d

110^2 ÷ 44^2 = 6.25

Let’s multiply the initial distance by this number.

d2 = 12 * 6.25 = 75 meters

This makes this problem easy to solve!

- JetDocLv 74 weeks ago
No. little Snowflake. This "question" is NOT typical of drivers license exams. It's more like a homework question from a physics class.

- derframLv 74 weeks ago
The amount of energy, and therefor the distance of the skid, is proportional to the square of the speed. So:

12 m * (110/44)² = 75 m