# Mistake Kinematics Problem

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?

#### Attachments

• Screen Shot 2014-05-18 at 6.22.57 PM.png
29.3 KB · Views: 362
• Screen Shot 2014-05-18 at 6.23.05 PM.png
34.8 KB · Views: 362

Doc Al
Mentor

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?
Looks like a mistake.

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

#### Attachments

• Screen Shot 2014-05-18 at 7.09.07 PM.png
33.7 KB · Views: 371
• Screen Shot 2014-05-18 at 7.09.14 PM.png
40.9 KB · Views: 370
Doc Al
Mentor
DocAl, is the speed also wrong in this problem? I think they made a mistake right at the end. They forgot to square root?
You are right. They made a mistake.

What book are you using?

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.

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...?

#### Attachments

• Screen Shot 2014-05-18 at 7.42.13 PM.png
65.7 KB · Views: 345
• Screen Shot 2014-05-18 at 7.42.39 PM.png
26.2 KB · Views: 341
Doc Al
Mentor
It's a bunch of review problems my teacher sent me "at our own risk."
I guess he didn't double check them for errors.

But, since I'm not really an ace in physics, I try to confirm the mistakes as much as possible.
Good idea. It's good practice.

Doc Al
Mentor
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.
Yes, another mistake.

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...?
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.