TIA E.

asked • 11/12/17# A bullet is fired upward reaches maximum height of 2500m. find out how long it would have taken to reach the height of 2500m

This is a numerical of physics which i cant solve so please help mee

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## 1 Expert Answer

Arturo O. answered • 11/12/17

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Assuming the bullet was fired from the ground, we need to solve for t in the equation

-4.9t

^{2}+ vt = 2500 mBut we first need to find the initial speed v, as Sean pointed out. We can find v from kinematics.

v

_{f}^{2}- v^{2}= 2ah_{max}v

_{f}= 0 [instantaneous rest at h_{max}]v = initial speed = ? [what we want to find]

a = -g = -9.8 m/s

^{2}h

_{max}= 2500 mv = √(2gh

_{max}) = √[2(9.8)(2500)] m/s ≅ √(49,000) m/sThen

h(t) = -4.9t

^{2}+ [√(49,000)]twith h in meters, t in seconds.

Now set h = 2500 m and solve for t.

2500 = -4.9t

^{2}+ [√(49,000)]t-4.9t

^{2}+ [√(49,000)]t - 2500 = 0You now have a quadratic equation in t, which you should know how to solve, and get

t ≅ 22.59 seconds.

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Sean H.

11/12/17