Asked by Mel
An object is thrown straight down off of a cliff with a velocity of 18m/s.
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?
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?
Answers
Answered by
hurrdurrbeedooda
Assuming 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.
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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