# The deceleration that causes a blackout and temporary blindness| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.8

### What deceleration of the rocket sled if it comes to rest in 1.1 s from a speed of 1000 km/h? (Such deceleration caused one test subject to black out and have temporary blindness.)

#### SOLUTION:

We can answer this question by referring to the definition of acceleration–change in velocity over change in time. That is

$a=\frac{\Delta v}{\Delta t}$

Before substituting the given values, the units should be homogeneous. We will convert 1000 km/hr to m/s.

$1000\:\frac{km}{hr}\times \frac{1000\:m}{1\:km}\times \frac{1\:hr}{3600\:sec}=277.7778\:m/s$

We substitute the values into the equation,

$a=\frac{277.7778\:m/s}{1.1\:sec}$

$a=252.5252\:m/s^2$

The deceleration is about 252.5252 meters per second per second.