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HW4 - l0 14-3 The 20-kg crate is subjected to a force...

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Unformatted text preview: l0 14-3. The 20-kg crate is subjected to a force having a constant direction and __a_magnitude F =100 N. where r is measured in meters. When .r= 4th.. the crate is . moving to the right: with a speed of 8 mls. Determine its speed when x = 25 m. The coeffioient of kinetic friction between the crate and the ground is m, = 0.25. Equation of Motion: Since the auto slides. the friction force devel- opedhctweentheeratcanditsoonucteurfnceis F} mmN 20.25 N. Applying Eq. 13-7, we have + t )3 F, = m,; N + room 30' '—20(9.8|) e 2(0) N =146.2 N TI + ZUl—I = T2 (7L £00m): +1oom30°t25 751 Principle of Want and E‘uargy: The horizontal omnponem of force F 1-i- which acts in the direction of displacement docs positive work. | 3 where: “friction force F; do” negative work since it acts in the "0‘25 “46.2)05 —w= “2'00,” opposite direction In that of disgheement. The mil reaction N. the - ' vertical component of force F and the weight of the crate do not displace hence do no work. Apnlfinfi Ea. guy. we have U =Ws [5 w" 19/ AM 13-11441. The force F, acting in a constant direction on fizthe 20-kg block, has a magnitude which varies with the . position 5 of the block. Determine how far the block slides - ‘ gig-before its velocity becomes 5 m/s. When 3 = 0 the block ' i'is moving to the right at 2 m/s. The coefficient of kinetic 'ffriCtion between the block and surface is m = 0.3. ' ' "‘ fin; . o; N, - 200.81) — 36031) = o F' I my)” 3 N, = 196.2 + so:2 ' 5% can. 1- ' _ 1“! Ii *SUI-a ‘ E I 4 I I I 5mm" + 3]; 50:2 d: - ”(19630) — 9.3]. an:2 a: = £030) (5)3 40+ 13.339-‘18363-33’ = 250 J" -s.596u-20.323 - o smtotthemlmytetds 3-3.41m Ans ...
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