## Measuring Uncertainty- Homework 1B.27

Jamie2002
Posts: 45
Joined: Wed Sep 30, 2020 9:55 pm

### Measuring Uncertainty- Homework 1B.27

A bowling ball of mass 8.00 kg is rolled down a bowling alley lane at 5.00 ± 5.0 m⋅s^−1. What is the minimum uncertainty in its position?

The textbook says the uncertainty in velocity is 5.00 m/s, but why? When given a number +/- another number, do we just disregard the second number (in this case the +/- 5.0 m⋅s^−1)? I was under the impression that if we were given an velocity of +/- x, the uncertainty would be |2x|.

Jamie2002
Posts: 45
Joined: Wed Sep 30, 2020 9:55 pm

### Re: Measuring Uncertainty- Homework 1B.27

Do we disregard the +/- 5.0 m/s^-1 because the problem calls for the minimum uncertainty?

Ayesha Aslam-Mir 2E
Posts: 45
Joined: Wed Sep 30, 2020 9:43 pm

### Re: Measuring Uncertainty- Homework 1B.27

I believe it gives one answer as you would only use the upper bound of the uncertainty you know to find the minimum value for the other.

In this case it looks like the textbook is only using the value within the range; knowing that the deltap deltav is a constant value in relation to h/4pi, maybe just using the center of that range would allow you to find the minimum in the next value (you're looking for position here I believe).

Jamie2002
Posts: 45
Joined: Wed Sep 30, 2020 9:55 pm

### Re: Measuring Uncertainty- Homework 1B.27

Wouldn't the uncertainty be 10 m/s, since it is (5 m/s + 5 m/s) - (5 m/s - 5 m/s)?

elena_chen_2B
Posts: 35
Joined: Wed Sep 30, 2020 10:09 pm

### Re: Measuring Uncertainty- Homework 1B.27

Jamie2002 wrote:Wouldn't the uncertainty be 10 m/s, since it is (5 m/s + 5 m/s) - (5 m/s - 5 m/s)?

I have this same question too. Is there a specific way to know when to multiply the +/- value by 2 and when to not when finding uncertainty?