# ps3c8 - Ph 111.01 Fall 2008 Solutions Problem set 3c(8...

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Ph 111.01 Fall, 2008 Solutions, Problem set 3c (8) Problem 1. In Denver, children bring their old jack-o-lanterns to the top of a tower and compete for accuracy in hitting a target on the ground (figure 4-18). Suppose that the tower height is h = [9.60] m, and that the bulls-eye's horizontal distance is d = [3.7] m from the launch point. If the pumpkin is thrown horizontally, what is the launch speed needed to hit the bulls-eye? (Neglect air resistance.) Figure 4-18 Solution. The time to fall a distance h under gravity, with no initial velocity in the vertical direction, is given by 2 1 00 2 2 1 2 y yyv t g t hg t =+ − =+− = giving () 2 1 2 2 29 .60 m 2 1.400 s 9.8 m/s gt h h t g = == = Then the horizontal velocity, which is constant, is given by ( ) 0 3.7 m 2.643 m/s 1.400 s xx x vv t == = = Problem 2 (Walker Ch. 5 P. 2). In a grocery store, you push a [15.5] kg shopping cart with a force of [10.5] N. If the cart starts at rest, how far does it move in 3.00 s? F m x m F G "" : x F ma x Fm a = =

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The figure above illustrates the three-fold approach to a problem: drawing, free- body diagram, and Newton's-law equations.
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ps3c8 - Ph 111.01 Fall 2008 Solutions Problem set 3c(8...

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