# Mistake Kinematics Problem

1. May 18, 2014

### alingy1

Why is it that they use 24 seconds for the time in b)? They get t=6.16s, why do they not plug that into the Dx equation to get 185m of x displacement?

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2. May 18, 2014

### Staff: Mentor

Looks like a mistake.

3. May 18, 2014

### alingy1

DocAl, is the speed also wrong in this problem? I think they made a mistake right at the end. They forgot to square root?

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4. May 18, 2014

### Staff: Mentor

You are right. They made a mistake.

What book are you using?

5. May 18, 2014

### alingy1

It's a bunch of review problems my teacher sent me "at our own risk."

But, since I'm not really an ace in physics, I try to confirm the mistakes as much as possible.

6. May 18, 2014

### alingy1

Another mistake spotted?

They made a mistake with the *10^4. Should be 10^3. Angles do not change (they are good).
The final velocity should be 12.07m/s, IE 43.45 km/h.

By the way, should we not express scientific notation with only numbers from 1 to 9? Why do they put 10.1 x 10^4 etc...?

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7. May 18, 2014

### Staff: Mentor

I guess he didn't double check them for errors.

Good idea. It's good practice.

8. May 18, 2014

### Staff: Mentor

Yes, another mistake.

As long as they do it right, it doesn't really matter. (Though you are correct.) But that's their first mistake: The momentum values are off by a factor of ten: they have 29.2 x 10^4 instead of 2.92 x 10^4, etc.

Good!