discussion_problems4 - DISCUSSION PROBLEM [4.1]: answer ......

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: DISCUSSION PROBLEM [4.1]: answer ... Assume wire is horizontal r F1 r F2 and consider a small section of wire in the middle: r w DISCUSSION PROBLEM [4.1]: As the wire is in equilibrium, i.e., no motion, then there is Why does a wire stretched between two posts always sag no net force, i.e., r r F1 = F2 in the middle no matter how tightly it is stretched? r r ... but there are no vertical components of F1 and F2 to r compensate w and produce no net vertical force. Therefore, our assumption that the wire is horizontal is r rr incorrect; clearly, to compensate for w , F1 and F2 must have vertical components. Therefore, they must “slope upward”, i.e., the wire must sag in the middle, viz: r F1 r w r F2 1 DISCUSSION PROBLEM [4.2]: ... answer ... DISCUSSION PROBLEM [4.2]: Yikes! What is the apparent weight of a person in an elevator if N (Upward force from scale) the cable breaks? w = mg (force due to Earth) From the free-body diagram N − mg = ma v , Yikes! so apparent weight N = m( g + a v ) = m( g + ( − g )) = 0 . Conceptually what’s happening is ... the floor and weighing scales are falling at the same rate as the person inside the car so there’s no net force on the weighing scale. This is what is popularly known as weightlessness (except, of course, you still have real weight!). 2 ...
View Full Document

This note was uploaded on 07/13/2011 for the course PHY 2048 taught by Professor Guzman during the Spring '08 term at FAU.

Ask a homework question - tutors are online