How many molecules are in 6.38g of h2o?

x = 2.2*10^23 molecules of H2O

Explanation:

H = 1g

O = 16g

H2O = 1g*2 + 16g

H2O = 18g = 1 mol of H2O

18 g___1 mol of H2O

6.38g__ x = 0.354 mol of H2O

1 mol6.22*10^23 molecules

0.354 mol__x = 2.2*10^23 molecules of H2O

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