first let us lay out the formula for potential
and kinetic energy:
pe = mgh
ke = (mv^2)/2
where: m=mass, v=velocity, g=gravitational
acceleration, h=height
calculating for mass using the known values of
pe:
340j = m (9.81 m/s^2) (50ft) (1m/3.28ft)
m = 2.27 kg
the law of conservation of energy states that
energy is neither created nor destroyed. therefore, the change in kinetic
energy from 50 ft to 35 ft would be equal to the change in potential energy
from 50 ft to 35 ft. however it would be opposite in signs since one is losing
while other is gaining.
ke(35ft) – ke(50ft) = - [ pe(35ft) – pe(50ft]
ke(50ft) = 0 since the brick is initially at rest
ke(35ft) = 340j - 2.27kg (9.81 m/s^2) (35ft)
(1m/3.28 ft)
ke(35ft)
= 102.38 j
