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Posted by **Mel** on Sunday, October 2, 2011 at 1:13pm.

a) What is the object's velocity after 15s?

b) If the cliff is 358m high, how long does it take for the object to hit the ground?

- physics -
**hurrdurrbeedooda**, Sunday, October 2, 2011 at 2:02pmAssuming acceleration is the force of gravity.

Vf = Vi + a*t

Vf = 18m/s + 9.81ms^-2 * 15s

Vf = 165.15 m/s

d = Vi*t + 1/2a*t^2

358 = 18m's*t + (1/2)9.81ms^-2 * t^2

Set it to zero:

0 = 4.91ms^-2 * t^2 + 18m/s * t - 358.

Use quadratic formula

t = 6.9s or t = -10.5s

Can't have negative time. Therefore it takes 6.9 seconds.

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