al physics

Time for upward motion = time for downward motion = 2s
Upward motion:
accleration = gsin 60
s = 1/2at^2 = 0.5 g sin 60 2^2 = 17.3m

2010-06-19 18:10:54 補充：
Sorry it should be
downward motion:
acceleration = gsin 60
s = 1/2at^2 = 0.5 g sin 60 2^2 = 17.3m

2010-06-19 20:51:13 補充：
Consider a ball being thrown vertically upwards, I guess you would agree that the time for upward journey is the same for downward journey.

2010-06-19 20:51:18 補充：
If we turn to the situation on inclined plane, the acceleration along the plane is always g sin60. In this case, the situation is exactly the same as a ball being thrown vertically upwards EXCEPT is acceleration is smaller than g.

2010-06-19 20:59:43 補充：
Hence, the time for upward motion is the same as the downward motion.
You can prove it mathematically , or more conveniently consider the velocity time graph of the ball (take upward as positive)

http://www.flickr.com/photos/27778998@N04/4714325636/

2010-06-19 20:59:51 補充：
Sometimes, it is VERY VERY useful to draw a graph and use graphical method to solve the problem, especially mc questions.