Question

Anne releases a stone from a height of 2 meters. She measures the kinetic energy of the stone at 9.8 joules at the exact point it hits the ground. What is the mass of the stone?

Answer 1

Eₖ = √1/2 mv²

Eₖ/v² = 1/2 m

2Eₖ/v² = m

mgh = 1/2 mv²

gh = 1/2 v²

2gh = v²

v = √2gh

= √2 × 10 N/kg × 2 m

= 6.324 ms⁻¹

m = 9.8/(6424)²

= 9.8/39.993

= 0.245 g

I am not sure if it's correct.

i transposed for m in the first equation then to find the velocity I combined the potential and kinetic energy equation. there was no mass because velocity doesn't depend on the mass

Then I used earth's gravitational field strength (g) 10 N/kg and the 2 m was the height provided in the question

you can try working and see if you get the same