SOLUTIONS TO GROUP QUIZZEZ 2

1301W.500 Quiz 2 Spring 2008 University of Minnesota ? m 2 m 1 F No friction One 8 2 1 × 11 cribsheet is allowed, as well as calculators. No textbooks or notebooks. This test carries 25 points which will be combined with individual test to give a grand total of 100 points. 2.g.3. A child puts a brick of mass m 2 on top of a brick of mass m 1 and pushes them up an inclined plane by exerting a constant force F parallel to the plane on the lower brick, as shown in the diagram. The plane is at an angle ? to the horizontal and there is no frictional force between the plane and the lower brick m 1 . The coefficient of static friction between the two bricks is ? s > tan ?. If the two bricks are to move together without slipping find: (a) corresponding acceleration of the blocks a (b) the maximum force F that the child can exert (c) the normal force N 1 exerted by the plane on brick m 1 Bonus part: How would your results change if the force F is applied in the opposite direction, i.e. if the child pushes the bricks down the plane? ? ???????? ?? ? ?? ??? ? ?? ? ???????? ?? ? ?? ??? ? ?? ??? cos)( cos)()sincos(sincos sin cos0 sin )1( )sincos( cos0 sin )2( :down Pushing cos)( cos)()sincos(sincos sin cos0 sin )1( ;)sincos( cos0 sin )2( :up Pushing ? ? ? ;,,,, 211 21112 112 121 211 22 222 211 21112 112 121 211 22 222 1 2max2121 gmmN gmmgmgmgm amgmNF NNgm NFgmam ga Ngm Ngmam gmmN gmmgmgmgm amgmNF NNgm NFgmam ga Ngm Ngmam NaF Nffaaamm sss s s s s sss s s s s ss += +=++?= =+?=? ? ? ? +??= ?+= ? +=? ? ? ? +?= += ? += +=?++= =++=? ? ? ? +??= ?+?= ? ?=? ? ? ? +?= +?= ? ??? ==== maz Microsoft Word - quiz2.3.s.doc