peter is holding a balloon .when he release the thread from rest,the balloon rises in to air.
at the moment the thread is just released,
1:the instantaneous speed of the balloon is zero.
2:the acceleration of the balloon is zero.
3:the net force acting on the ball is zero
a.1only
b:3only
c:1and2 only
d:2and3 only
答案係a
點解第3唔岩? 佢係release from rest 點解net force 唔係zero?
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2009-01-17 7:01 am
回答 (2)
2009-01-17 7:46 am
✔ 最佳答案
The answer is a.
When the thread is released, the upthrust acting on a balloon is greater than the weight of the balloon. Therefore, an upward net force acts on the balloon. The balloon is accelerating upwards from rest.
1. correct
The balloon is accelerating upwards from rest. When the thread is just released, the initial velocity is 0.
2. incorrect
The balloon is accelerating upwards. This is because an upward net force is acting on the balloon as the upthrust is greater than the weight of the balloon.
3. incorrect
An upward net force is acting on the balloon as the upthrust is greater than the weight of the balloon.
=
2009-01-17 7:19 am
因為有個gravitational force 拉住個ballon, 所以net force is non-zero
收錄日期: 2021-04-29 18:15:46
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