Unformatted text preview: l0 143. The 20kg 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. 137, 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 1i
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 1311441. The force F, acting in a constant direction on ﬁzthe 20kg block, has a magnitude which varies with the . position 5 of the block. Determine how far the block slides  ‘
gigbefore 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 *SUIa ‘ E
I 4 I I I
5mm" + 3]; 50:2 d:  ”(19630) — 9.3]. an:2 a: = £030) (5)3 40+ 13.339‘1836333’ = 250
J" s.596u20.323  o smtotthemlmytetds 33.41m Ans ...
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 Spring '08
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