F.5 phy projected motion(2)

YTC

2014-10-25 10:37 pm

Picture: http://postimg.org/image/f2gw046n3/
A bomber flying horizontally at a velocity of 100m/s is going to bomb a site 1km
below.
What is the horizontal distance between the bomber and the site when the bombs are released?
What is the speed of the bomb just before it hits the site?
Please help me!thank you!

回答 (1)

天同

2014-10-26 1:40 am

✔ 最佳答案

Let T be the time of flight of the bomb before hitting the site.
Consider the vertical motion of the bomb,
Use equation: s = ut + (1/2)at^2
with s = 1000 m, u = 0 m/s, a = g(=10 m/s^2), t =T
hence, 1000 = (1/2)(10)T^2
T = 14.14 s

Therefore, horizontal distance between bobmber and the site
= 100 x 14.14 m = 1,414 m

Use equation: v^2 = u^2 + 2as for the vertical motion of the bomb
with u = 0 m/s, a =g(= 10 m/s^2), s = 1000 m, v =?
hence, v^2 = 2(10).(1000) (m/s)^2
v = 141.4 m/s

Therefore, speed of bomb just before hitting the site
= square-root[100^2 + 141.4^2] m/s = 173 m/s

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