142_Physics ProblemsTechnical Physics

142_Physics ProblemsTechnical Physics - 144 The Laws of...

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144 The Laws of Motion (c) From above, Q = 800 . N and P = 14 0 . N. (d) The 3-kg block models the heavy block of wood. The contact force on your back is represented by Q , which is much less than the force F . The difference between F and Q is the net force causing acceleration of the 5-kg pair of objects. The acceleration is real and nonzero, but lasts for so short a time that it never is associated with a large velocity. The frame of the building and your legs exert forces, small relative to the hammer blow, to bring the partition, block, and you to rest again over a time large relative to the hammer blow. This problem lends itself to interesting lecture demonstrations. One person can hold a lead brick in one hand while another hits the brick with a hammer. P5.55 (a) First, we note that FT = 1 . Next, we focus on the mass M and write TM g 5 = . Next, we focus on the
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