仲有一條力學題 - Ans.fyi 參考答案

仲有一條力學題

Curtis

2007-01-01 6:19 am

An object, moving up a smooth inclined plane making an angle a with horizontal decreases its speed from x to y m/s. What is the distance, in metres, travelled in this period?
我計到果答案係(y^2-x^2)/(2gsina)
但係果正案確案係(x^2-y^2)/(2gsina)
係個答案錯定係個我計錯？（應該都係後者多__）

回答 (1)

abcsghk

2007-01-01 6:43 am

✔ 最佳答案

The component of weight along the inclined plane
= mg sin a

By Newtons Second Law,
F = m A 【I use capital A to avoid confusion with the angle a】
mg sin a = m A
A = g sin a【uniform acceleration】

Apply the formula v² = u² + 2As
y² = x² + 2 (-g sin a) s
y² - x² = -2 g sin a s
s = (y² - x²) / (-2 g sin a)
s = (x² - y²) / (g sin a)

So the answer in the book is correct.

Your problem may be because you have forgotten to add a negative sign to the acceleration because the acceleration is in the opposite direction as its motion.

Hope it helps!
Wish you a Happy 2007!

參考: Myself

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