The initial mechanical energy is the potential energy (PE) which can be solved through the equation,
PE = mgh = (40 kg)(9.8 m/s²)(12 m) = 4,704 J
The energy at the bottom is the kinetic energy and can be calculated through the equation,
KE = 0.5mv² = (0.5)(40 kg)(10 m/s)² = 2000 J
Therefore, she lost 2,704 J of energy due to friction
Answer: t = 10s
Explanation:
Assuming there's no air resistance,
Initial velocity (u) = 0 m/s
Acceleration by gravity (a) = 9.81 m/s^2
Displacement (s) = 500m
Time taken (t) = ?
Now,
Use formula,
s = u×t + (1/2)×a×t^2
s = 0×t + (1/2)×9.81×t^2
500 = 4.905×t^2
t = 10s
It's the distance between the middle of the lens to the focus.