Question

What is the 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.)

Question Image

**Figure 4.31**Rocket sled.

$-2.5 \times 10^{2}\textrm{ m/s}^2$

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This is College Physics Answers with Shaun Dychko. The rocket's light is going to decelerate from an initial speed of 1000 kilometers an hour. We'll convert that into meters per second because we usually need mks units for our formulas, meters kilograms, and seconds. So we'll turn those kilometers per hour into meters per second by multiplying by one hour for every 3600 seconds, which makes seconds in the denominator. Then times by 1000 meters for every kilometer, which puts meters in the numerator, and so we have 277.78 meters per second. It's usually nice to take care of this unit conversion business in this first step when you're writing down the information given so that we don't have to think about it later. The time for deceleration is 1.1 seconds and the final speed is zero. So we're bringing this slide to a stop. The acceleration that the sled and the occupant inside will experience is the change of velocity divided by time. That's the final velocity minus initial velocity divided by time, zero minus 277.78 meters per second divided by 1.1 seconds, which is 2.5 times 10 to the 2 meters per second squared. Now, you might want to say this is negative, I suppose, if you're going to say that the initial velocity to the right is positive.