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I-loveyou 2012-5-13 04:05 PM

PHYSICS LINEAR MOTION

A ballast bag is dropped from a balloon that is 300m above the ground and rising at 13m/s. For the bag, find
a) the maximum height reached
b) its position and velocity 5s after being released, and
c) the time before it hits the ground.

我想問PART A 個答案係唔係313丫 ?
之後B個問題有D唔明 -3-''
跟住C係點計 ?
THX~~

14c14c 2012-5-14 08:15 PM

take upward as positive
a.v^2-u^2=2as
0^2-13^2=2(-10)s
s=8.45
maximum height : 300+8.45 = 308.45 m above ground

b.s=ut+0.5at^2
s=13(5)+0.5(-10)(5)^2
s=-60
position: 300-60=240 m abouve ground

c.s=ut+0.5at^2
-300 = 13t+0.5(-10)t^2
5t^2-13t-300=0
t=9.1543 s or t=-6.5543s(rejected)
time taken:9.1543s
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