2008BAP 1 Solutions

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Unformatted text preview: served. Visit the College Board on the Web: www.collegeboard.com. AP PHYSICS B 2008 SCORING GUIDELINES Question 2 15 points total (a) 4 points For a correct application of Newton's 2nd law for the two-block system F = ( m A + m B )a Note: Newton's 2nd law may be applied to each block separately to produce an equivalent solution. For a correct determination of the acceleration F 4.0 N a= = ( m A + mB ) (2.0 kg + 8.0 kg ) 1 point Distribution of points 1 point a = 0.40 m s2 For correct substitution of the acceleration into Newton's 2nd law for one of the blocks Fspring = m Aa (or F - Fspring = mB a ) For the correct solution (consistent with the value of the acceleration found above) 1 point 1 point Fspring = (2.0 kg ) 0.40 m s Fspring = 0.80 N ( 2 ) (or Fspring = 4.0 N - (8.0 kg ) 0.40 m s ( 2 )) Note: A correct free-body diagram for each block could earn 1 point each. (b) 2 points For a correct expression relating spring force to extension Fspring = kx For the correct solution using the spring force from part (a) Fspring 0.80 N x = = k 80 N m x = 0.010 m (c) 3 points For correctly indicating that the acceleration will be the same as before For a correct justification (only if the previous point was awarded) Examples: Explaining that in both cases there is a 4.0 N force pulling a combined mass of 10 kg, and hence the acceleration will be the same in the two cases. (Note: One point was awarded when the student noted that either the net force acting on the system of two blocks or the mass of the system is unchanged. For full credit, the student must have noted that both the force and mass are the same in the two cases.) Applying Newton's 2nd law to each block and calculating an acceleration with the same value as in part (a). 1 point 2 points 1 point 1 point 2008 The College Board. All rights reserved. Visit the College Board on the Web: www.collegeboard.com. AP PHYSICS B 2008 SCORING GUIDELINES Question 2 (continued) Distribution of points (d) 3 points For correctly indicating that the spring extension is greater than in part (b) For a correct justification (only if the previous point was awarded) Examples: The spring force on the 8.0 kg block pr...
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This note was uploaded on 02/09/2011 for the course PHYS 10 taught by Professor Davidnewton during the Spring '11 term at DeAnza College.

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