247_Physics ProblemsTechnical Physics

# 247_Physics ProblemsTechnical Physics - Chapter 8*P8.74(a...

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Chapter 8 249 *P8.74 (a) Conservation of energy for the sled-rider-Earth system, between A and C: KU K U mm m v v ig ifg f += + + =+ = 1 2 25 980 976 1 2 0 2980 141 2 2 2 .. . . . ms m m 2 C C 2 bg ej af FIG. P8.74(a) (b) Incorporating the loss of mechanical energy during the portion of the motion in the water, we have, for the entire motion between A and D (the rider’s stopping point), KU fxK U i k fg f +− : 1 2 80 2 5 80 9 80 9 76 0 0 2 kg m s kg m s m 2 b g a f . = + fx k −= × k 790 10 3 . J (c) The water exerts a frictional force f x k = × = ×⋅ = 7 90 10 7 90 10 158 33 J N m 50 m N and also a normal force of nm g == = 80 9 80 784 kg m s N 2 . The magnitude of the water force is 158 784 800 22 N N N (d) The angle of the slide is θ ° sin . . 1 10 4 m 54.3 m For forces perpendicular to the track at B,
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