A100-kg boulder sits on the top of a 50-meter high cliff. it falls off. how fast is it traveling just before it hits the ground?

a. 31 m/s

b. 490 m/s

c. 98 m/s

d. 245 m/s

m = mass of the boulder = 100 kg

h = height of the cliff from which boulder falls = 50 m

g = acceleration due to gravity = 9.8

v = speed of boulder just before it hits the ground = ?

Using conservation of energy

Kinetic energy of boulder just before hitting the ground = Potential energy of boulder at the top of cliff

(0.5) m v² = mgh

dividing both side by "m" , "m" cancel out and we get

(0.5) v² = gh

inserting the values

(0.5) v² = (9.8) (50)

v = 31

Hence correct choice is A. 31 m/s

this is poiselle's equation from fluid mechanic in physics. mech eng

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explanation: