# 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

### 2 個解答

• 最愛解答

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),

==&gt; v = at

==&gt;咁因為大家的時間都係一樣, 而個acceleration 都係一樣,

==&gt; 所以佢地個v 都會係一樣

再用第二條式(v^2-u^2=2as)

==&gt; u=0, v and a is the same,

==&gt;所以s 都會係一樣

==&gt; 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

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

==&gt; 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

• 登入以回覆解答
• the answer is A. because only if it has more energy before it falls it will fall faster

also because

B. it can&#39;t be chemical energy

C. It does&#39;t heat up

D. the balls don&#39;t produce energy

• 登入以回覆解答