Collisions - did I solve correctly

[haki]

Hi,
I would like somebody to verify if I have correctly solved a problem.
The problem is this: Rock of mass m falls from height 20 m to the ground. What is the average force of the ground acting on the rock if it takes 0.025 s to bring the rock to full stop. Express the force in relation to the mass of the rock.
Keywords that came to my mind are: Collisions, momentum, impusle, mom.-impul. theorem.
The trick should be in expressing the 2nd Newton law with momentum.
F = m*a is equivalent to F = p/t.
To get the momentum p. I would use energy conservation. all the potential energy goes to the kinetic energy just before the collision:
m*g*h=1/2*m*v^2 -> v = sqrt(2*g*h) soo
F = p/t
p=v*m
v=sqrt(2*g*h)
Solution:F= sqrt(2*g*h)*m/t Putting the numbers in it would get us:
F = sqrt(2*9.8*20)*m/0.025 = 729 * m
Was my resoning correct?

 

[finchie_88]

Yer, what you've done looks right

 

[quicknote]

Hi there,
Your reasoning and solution seem to be correct. You have correctly applied the principles of momentum and energy conservation to solve the problem. Additionally, your use of keywords such as collisions, momentum, impulse, and the momentum-impulse theorem show a good understanding of the topic. Keep up the good work!