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# The speed of a particle after an explosion is given by the formula A =

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Math Expert
Joined: 02 Sep 2009
Posts: 43804
The speed of a particle after an explosion is given by the formula A = [#permalink]

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07 Sep 2017, 22:37
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Difficulty:

15% (low)

Question Stats:

90% (01:17) correct 10% (01:58) wrong based on 30 sessions

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The speed of a particle after an explosion is given by the formula A = 15c/t^2, where c is a constant, t is the time after explosion, and A is the speed of the particle, in feet per second, at t time after the explosion. If the speed of a particle at 2 seconds is 450 feet per second, what is the speed of the particle, in feet per second, at 3 seconds?

A. 400
B. 300
C. 250
D. 200
E. 100
[Reveal] Spoiler: OA

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Re: The speed of a particle after an explosion is given by the formula A = [#permalink]

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07 Sep 2017, 23:43
We have been given $$A = \frac{15c}{t^2}$$
where c is a constant, t is the time after explosion, and A is the speed of the particle, in feet per second(at t time after the explosion)

Since, the speed is 450 ft/s at t=2,
substituting these values,

$$450 = \frac{15*c}{2^2}$$
Constant(c) = $$\frac{450 * 4}{15} = 30 * 4 =120$$

Now, we have been asked to find A given t=3
Therefore A(when t=3) = $$\frac{15*120}{3^2} = 5*40 = 200$$(Option D)
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Re: The speed of a particle after an explosion is given by the formula A =   [#permalink] 07 Sep 2017, 23:43
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