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# finding height and also kinetic energy 2 quick questions watch

1. bit stuck please help me out. these got covered too quickly in lesson and cant understand my notes.

1.) an object falls from rest through a height H to hit the ground with a speed of 25ms-1. using energy considerations and assuming there is no air resistance, find H.

a seperate question

2.) a stone of mass 0.8kg is dropped from a height of 1.5m into a pond. Find the kinetic energy of the stone as it hits the water. the stone then begins to sink in the water with a speed o 2.1ms-1. determine the kinetic energy lost when the stone strikes the water.
2. 1) Just plug all the information you have into a SUVAT formula:
V=25 U=0 A=9.8 S=?
V²=U²+2AS

V=? U=0 A=9.8 S=1.5
V²=U²+2AS
And when you get V put it into
Kinetic Energy=1/2MV²
M=0.8 V=?

To find the kinetic energy lost put 2.1 into the equation as V and subtract the answer you get from your original answer for the stone's kinetic energy
3. thats really helpful i agree with it all.

however in no.1 is there another way as it says using energy considerations?
4. 1/2mv^2=mgh
1/2v^2=gh

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