PHYSIC 問題

👨🏻‍🏫 學術台其他 - 科學

KBC

2012-05-03 8:52 pm

A child jumps vertically upwards, leaving the ground with speed 9.81ms^-1, How long does it remain in the air? For the purposes of this question, you may treat the child as particle, subject only to the downward force of gravity. Please aadvise me more details! Thanks!

更新1:

what means how long does it remain in the air? please advise me 中文??

更新2:

i dont understand 1s x 2 = 2s??

回答 (1)

天同

2012-05-03 11:27 pm

✔ 最佳答案

You are asked to find the time interval between the child leaves the ground and when he hits the ground again.

Use equation of motion: s = ut + (1/2)at^2
with s = 0 m, u = 9.81 m/s, a = -g (= -9.81 m/s^2), t =?
Hence, 0 = (9.81)t + (1/2).(-9.81)t^2
i.e. t = 2 x 9.81/9.81 s = 2 s

Therefore, the child remains in air for 2 seconds.

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