07. what is the velocity of a 500kg elevator that has 4000j of energy?
1) givens & unknown:
2) formula:
3) sub & solve:

v = 4 m/s

Explanation:

Given data:

Mass of elevator = 500 kg

Energy = 4000 j

Velocity = ?

Solution:

1/2 mv²  =  4000 j

1/2 (500 kg)v²  =  4000 j

v²  =  4000 j×2 / 500 kg

v²  =  4000 kg. m²/s² ×2 /  500 kg

v²  = 8000 kg. m²/s² /  500 kg

j =  kg. m²/s²

v²  = 16 m²/s²

v = 4 m/s

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g