• Support PF! Buy your school textbooks, materials and every day products Here!

Object hung from two ropes - determine weight

  • Thread starter bcalkins
  • Start date
  • #1
19
0
Original Problem:
sin(45)(425N) + sin (60)(601N) = 821N
The problem is, no scale is perfect. Let's assume for the time being that the angles are quite accurate, but you know based on your past experience that these scales can be off by as much as 2 N. This uncertainty propagates through any calculation that involves the measured quantities.

By how much (in N) could your estimation of the weight of the box be off?

Hint: The easiest way to do this is by finding the highest and smallest possible values of the weight that can result from the range of values of the measured forces.

What I'm doing - but wrong answer:
sin(45)(423) + sin(60)(599) = 817.8553853
sin(45)(427) + sin(60)(603) = 824.147914
Subtract higher from lower = 6.29300

Where am I going wrong?
 

Answers and Replies

  • #2
172
2
Let me try re-phrasing the question: How much do the maximum and minimum values differ from the calculated weight?

The value you found (6.29) is the difference between the maximum and minimum values. Neither value (min or max) will actually differ from the real weight by that much, since the real weight is somewhere in the middle.
 
  • #3
19
0
So would the correct answer be 6.29/2=3.14?
 
  • #4
172
2
Actually, the minimum and maximum don't differ from the calculated weight by the same amount. One value has slightly more error than the other. Try finding the difference between the calculated weight and each of the min/max values.
 

Related Threads for: Object hung from two ropes - determine weight

  • Last Post
Replies
19
Views
1K
Replies
10
Views
617
  • Last Post
Replies
6
Views
7K
Replies
7
Views
3K
  • Last Post
Replies
0
Views
20K
  • Last Post
Replies
7
Views
229K
  • Last Post
Replies
2
Views
7K
  • Last Post
Replies
5
Views
5K
Top