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標題:
montion and force
發問:
for this question , take g=10 Firework X are designed to explode at the height of 200m , find the velocity of firework X when it is fired .
Use equation of motion: s = vt - (1/2)at^2 with s = 200 m, a = -g(=-10 m/s2), v = 0 m/s, t =? hence, 200 = -(1/2)(-10)t^2 i.e. t = 6.325 s Then use equation of motion: v = u + at with v = 0 m/s, a = -10 m/s2, t = 6.325 s, u =? hence, 0 = u + (-10)(6.325) i.e. u = 63.25 m/s The velocity of the firework is 6.325 m/s when it is fired. 2011-09-17 14:10:19 補充： sorry, a typo in the naswer, it should read: "The velocity of the firework is 63.25 m/s when it is fired."
其他解答:
由於問題冇叫你去計t,所以唔使咁煩去計t先,可以直接用公式v^2=u^2+2as 以向上為正 v^2=u^2+2as 0=u^2-4000u^2=4000 u=63.25m/s 所以初速度係63.25m/s向上考試個陣要靈活運用個四條公式,清楚個四條公式唔需要D咩,如v^2=u^2+2as就唔需要知道時間t,係唔需要求時間ge題目入面,用E條就最啱. 如果唔係,浪費時間之餘,仲有更大機會計錯4E350C6F8B48ECA2
montion and force
發問:
for this question , take g=10 Firework X are designed to explode at the height of 200m , find the velocity of firework X when it is fired .
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最佳解答:Use equation of motion: s = vt - (1/2)at^2 with s = 200 m, a = -g(=-10 m/s2), v = 0 m/s, t =? hence, 200 = -(1/2)(-10)t^2 i.e. t = 6.325 s Then use equation of motion: v = u + at with v = 0 m/s, a = -10 m/s2, t = 6.325 s, u =? hence, 0 = u + (-10)(6.325) i.e. u = 63.25 m/s The velocity of the firework is 6.325 m/s when it is fired. 2011-09-17 14:10:19 補充： sorry, a typo in the naswer, it should read: "The velocity of the firework is 63.25 m/s when it is fired."
其他解答:
由於問題冇叫你去計t,所以唔使咁煩去計t先,可以直接用公式v^2=u^2+2as 以向上為正 v^2=u^2+2as 0=u^2-4000u^2=4000 u=63.25m/s 所以初速度係63.25m/s向上考試個陣要靈活運用個四條公式,清楚個四條公式唔需要D咩,如v^2=u^2+2as就唔需要知道時間t,係唔需要求時間ge題目入面,用E條就最啱. 如果唔係,浪費時間之餘,仲有更大機會計錯4E350C6F8B48ECA2
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