Acceleration of rock due to gravity

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SUMMARY

The discussion focuses on calculating the acceleration of a rock dropped from a height of 125 cm due to gravity. The final velocity upon impact is determined to be 49.5 m/s, and the time taken to reach the ground is 5.05 seconds. The participants suggest using either the conservation of energy principle or kinematic equations to derive these results, specifically referencing the equation v = u + at, where initial velocity (u) is 0 m/s and acceleration (a) is 9.81 m/s².

PREREQUISITES
  • Understanding of basic kinematics
  • Familiarity with gravitational acceleration (g = 9.81 m/s²)
  • Knowledge of conservation of energy principles
  • Ability to apply kinematic equations
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A rock is dropped from rest at the top of a cliff 125 cm high.

a) At what speed does it strike the ground?

b) How long does it take?



To find the velocity the equation used is v = u + at

I know that (u = 0) as it's from rest and g = 9.81 ms (gravity)

But I just need help on how to get the velocity when the time is not stated!

I have the answers but I'm not sure how to reach them

a) 49.5 ms

b) 5.05 ms
 
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You have two options:

(1) Use conservation of energy

(2) Use another kinematic equation which involves velocity, distance and acceleration
 

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