# Homework Help: Average acceleration of Suzie stopping with roller blades

1. Dec 22, 2007

### rr92890

Suzie (of mass 52kg) is roller blading down the sidewalk going 36 mph. She notices a group of workers down the walkway who have unexpectedly blocked her path, and she makes a quick stop in 1.9 seconds. What is Suzies average acceleration? Answer in m/s^2. What force was exerted to stop Suzie? Answer in N.

I had converted miles to meters and divided it by the time in order to get the average, but the answer was incorrect. and for the second question I had multiplied the average by the weight, but that was also incorrect.

2. Dec 22, 2007

### Staff: Mentor

That part sounds right. Show exactly what you did.
That's not quite correct.

3. Dec 22, 2007

### cryptoguy

did you convert hours to seconds? Aavg = delta V / delta t; so what you did should work..

4. Dec 23, 2007

### rr92890

I changed 36 miles per hour to .01 miles per second which converts to 16.09344 meters per second. I divided that by 1.9 which equals 8.470231579 as the average acceleration. Then for the second part 8.470231579*52 = 440.4520421 N as the force exerted. I'm pretty sure that is what I did.

5. Dec 23, 2007