Question

af - Adobe Acrobat Reader DC 9 - Conservatio... * Q 110 o 75% Experimenti - I. Work done on system Experiment 1: Two identical blocks, A and B, are initially at rest on a level, frictionless table. At time tots hands push the blocks toward each other as shown at right. Each hand exerts a constant horizontal force of magnitude F At time tots, each block has moved a distance de from its initial position. A. During the interval from t, tot 1. is the work done on block A by the hand positive, negative, or zero? Explain 1-12 2. Is the work done on block B by the hand positive, negative, or zero? Explain. The sum of the work done by all external forces exerted on an object or system is called the network by external forces, W . Other symbols used in this lab include K, U, and for kinetic energy potential energy, and total energy as well as indicating the change (final-initial). B. Consider system 1. consisting of blocks A and B. Write an expression for the network done on system 1 by external forces during the interval from t, to ty in terms of the given quantities. Explain. C. Write an expression for the net force on system 1 at an instant between t, and ty. Could you use this net force to calculate the net work on system 1 by external forces? Explain. D. Consider the following statement: "Since both block move the same distance, but in opposite direotions, the system hasn't really moved. Therefore, the network on the system is zero." Do you agree or disagree with this statement? Explain. In your own words, explain what displacement(s) should be used to calculate the network on a system in which different parts of the system undergo different displacements. arch

Answer 1

Positive Work

• If a force displaces the object in its direction, then the work done is positive
  So, W=Fd
• Negative work
• If the force and the displacement are in opposite directions, then the work is said to be negative.

(A) d) Work done on block A t-t, A WA= Fid Casoo = F. d. The work done is positive, (2) Work done on block B, tate A B We = + (d). Caso" = Fid. The work done is positive, (③) The net woord done on the system by ext. forces, Wner ent. = work done on À & work done on 'B' = Fod trod = 2 Fod. (C) The net fonce on the system I 1 Fret = force on À force on B' (as the dine from = to t (fo) = 0 of the fonces. are opposite ? We can not use this net fornce for calculating the a r net work done as the direction of the forces are opposite and equal that brings the net work done equals to zeno, which is actually not Zeno (o).