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freely falling bodies ?
A ball is thrown straight upward and rises to a maximum height of 25 m above its launch point. At what height above its launch point has the speed of the ball decreased to one-half of its initial value?
did they give me enough info? i can't figure this out.
5 Answers
- Anonymous1 decade agoFavorite Answer
Working formula is
Vf^2 - Vo^2 = 2gh
where
V = final velocity = velocity of ball at its max height = 0
Vo = initial velocity
g = acceleration due to gravity = 9.8 m/sec^2 (constant)
h = maximum height attained by ball = 25 m (given)
Substituting values,
0 - Vo^2 = 2(-9.8)(25)
NOTE the negative sign attached to the acceleration due to gravity. It simply means that the ball loses its speed as it goes up.
And, solving for Vo,
Vo = 22.14 m/sec.
Let
s = height where the speed of the ball is half of its original value
and using the same formula above,
Vf^2 - (22.14)^2 = 2(-9.8)(s)
Since Vf = (1/2)(22.14) = 11.07, then the above simplifies to
(11.07)^2 - (22.14)^2 = -19.6(s)
and solving for "s"
s = 18.75 m.
Hope this helps.
- RetsumLv 61 decade ago
We can find the launch speed from
v^2 - u^2 = 2as
At max height v = 0
-u^2 = -2g x 15
u = SQRT(50g)
Now v = (1/2)u = (1/2)SQRT(50g)
From v^2 - u^2 = 2as
s = (v^2 - u^2)/-2g = -[(3/4) x 50]/-2 = 18.75 m
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- OldPilotLv 71 decade ago
Yes. Figure forwards to get original velocity then backwards to get height
d = 0.5 AT^2
25 = 0.5 * 9.8 m/s^2 * T1^2 solve for T1
Then
V = AT1
V1 = 9.8 * T (from above) Solve for V1
V2 = V1/2 Solve for V2
V2 = AT
V2 = 9.8 * T2 solve for T2
d2 = 0.5 * A*T2^2 Solve for d2
d2 = 0.5*9.8*T2^2
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- ?Lv 45 years ago
equation v^2=u^2+2as preliminary velocity u=0, then v^2=2gh(a=g,s=h) at top h, permit v be the fee then v^2=2gh .........eq a million at some top h1,it somewhat is velocity 2v strengthen into doubled then (2v)^2=2gh1 4(v^2)=2gh1 by making use of eq a million 4(2gh)=2gh1 cancelling 2g we get h1 =4h