Question

it takes 6 sec for a stone to fall the the bottom of a mineshaft. calculate the
depth of the shaft

Answer 1

ok so this is simple projectile motion problem.

if we have an object falling in free fall it is subject to gravity of -9.80m/s^2

so it says it takes 6 sec to fall and we know initial velocity was zero so we know that h=vt+1/2gt^2 so we get h=0+1/2*9.80*6^2 = 176.4m 

so solving for final speed we get KE=PE = 1/2mv^2=mgh = 1/2v^2=gh so 
v=sqrt(2*g*h) = sqrt(2*9.8*176.4m) = 58.8m/s final speed when it hits the ground


hope this helps you! Thanks!!