Question

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Answer 1

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ÒÑÖª${v}_{t}^{\;}=5m/s$    ${v}_{0}^{\;}=20m/s$     $a=-5m/{s}_{\;}^{2}$
ÓÉ${v}_{t}^{2}-{v}_{0}^{2}=2as$
µÃs=$\frac{{v}_{t}^{2}-{v}_{0}^{2}}{2a}=\frac{{5}_{\;}^{2}-2{0}_{\;}^{2}}{2¡Á£¨-5£©}$=37.5m
£¨2£©Éè¼õËÙʱ¼äΪ${t}_{1}^{\;}$£¬ÔÈËÙʱ¼äΪ${t}_{2}^{\;}$
ÒÑÖª${v}_{t}^{\;}=5m/s$     ${v}_{0}^{\;}=20m/s$    $a=-5m/{s}_{\;}^{2}$
ÓÉ${v}_{t}^{\;}={v}_{0}^{\;}+at$
µÃ${t}_{1}^{\;}=\frac{{v}_{t}^{\;}-{v}_{0}^{\;}}{a}=\frac{5-20}{-5}s=3s$
ÒÑÖªs=15m   $\overline{v}=5m/s$
ÓÖÓÉ$s=\overline{v}•{t}_{2}^{\;}$
µÃ${t}_{2}^{\;}=\frac{s}{\overline{v}}=\frac{15}{5}s=3s$
¹Ê${t}_{×Ü}^{\;}={t}_{1}^{\;}+{t}_{2}^{\;}=3+3=6s$
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