4. Which of the following statements are true?
(1) The direction of external force acting on an object is the same as that of the acceleration of the object.
(2) The velocity and the acceleration of an object are always in the same
direction.
(3) If the velocity of an object is very large at a certain instant, then the accleration at that instant must be very large.
a. (1) only
b. (2) only
c. (1) and (2) only
d. (1) and (3) only.
can you give an explaination?
2 mc about mechanics
2007-08-14 12:17 am
回答 (1)
2007-08-14 1:44 am
✔ 最佳答案
the answer is B .. 1) is incorrect because the external force is perpendicular to acceleration in circular motion.
3) is incorrect because the acceleration = change of velocity in certain time intervals , if the change of velocity is keep constant , the acceleration also constant , so LARGE velocity in certain instant won't cause large acceleration .
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