? 發問於 科學及數學其他 - 科學 · 1 十年 前

science(energy)

Two idential balls(A & B )fall at the same time.Ball A reaches the ground at a greater speed. This shows that

A.ball A has more potential energy than ball B beforethey fall

B. Ball A has more chemical energy than ball B before they fall

C. Some energy in ball B is coverted into heat energy

D. More energy is produced in ball A than that in ball B

個答案係咩?點解既?

更新:

用中文答都得

2 個解答

評分
  • 1 十年 前
    最佳解答

    假設係地球上面發生, 而個gravitational field is constant, 咁兩個同樣的波係同一時間一齊放手 (release from rest), 如果再neglect 埋air resistance effect, 咁樣理論上係會係同樣時間著地的.

    因為佢地之間只係關係到kinematics , 即係 v = u+at; v^2-u^2=2as; s=ut +1/2at^2 等等.....

    就今次來講呢, 我地可以用v = u+at 同 v^2-u^2=2as 來解釋.

    因為大家都係release from rest, 所以大家的u 也是0, 用第一條式(v = u+at),

    ==> v = at

    ==>咁因為大家的時間都係一樣, 而個acceleration 都係一樣,

    ==> 所以佢地個v 都會係一樣

    再用第二條式(v^2-u^2=2as)

    ==> u=0, v and a is the same,

    ==>所以s 都會係一樣

    ==> 咁即係話佢地的displacement travel 係一樣, 但係現在其中一個波早d 到地下

    ==> 由呢一樣野就可以deduce 到 兩個波的inital height 係唔一樣

    ==> 所以兩個波的inital potential energy 都唔同啦

    我講咁多野都係想你知道點解, 而唔係只係記得個答案. 始終 Method 緊要過 answer 好多啦.

    2007-03-13 12:45:26 補充:

    又有另一個答法會簡單d. 就係諗吓個total energy. BALL A 係撞地時velocity 大過 BALL B (即係同一高度的時候, ball A 的 kinetic energy 大過 ball B)== that means the totally energy on Ball A is larger== therefore, if all the energy is stored as potential energy== ball A mush higher than ball B since U = mgh

  • 1 十年 前

    the answer is A. because only if it has more energy before it falls it will fall faster

    also because

    B. it can't be chemical energy

    C. It does't heat up

    D. the balls don't produce energy

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