Mistakes in Kinematics Problem: A Lesson in Precision and Accuracy

[alingy1]

Please look at pictures.

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?

 

[Doc Al]

Please look at pictures.

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.

 

[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?

 

[Doc Al]

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?

 

[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.

 

[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...?

I'll refer this page to my class. They'll be glad :)

 

[Doc Al]

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]

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.

I'll refer this page to my class. They'll be glad :)

Good!