1.A lever does 765 J of work and the person using the lever applies 900 J of work. What is the efficiency of the lever? 2.When your car gets a flat tire, you need to use a jack to lift the car. The car requires only 9000 J of work to lift it, but due to the inefficiency of the jack, you need to put in 15,000 J of work to lift the car. What is the efficiency of the jack?

3.An automobile gasoline engine can do 225 J of work with each stroke of its pistons. If the engine has an efficiency of 30%, what is the amount of work that must be done on the pistons in the engine?

second mirror gathers light from a faraway object and reflects it to another mirror. - a.

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  1.the balanced   chemical equation is as below

cu +   2 ag(no)₃ → cu(no₃)₂   +2 ag

2.the   much silver   produced   is   50.9 g

step 1: find the   moles of cu

moles =   mass÷   molar mass

  from periodic table the molar mass of cu = 63.5 g/mol

moles is therefore = 15.00 g÷ 63.5 g/mol = 0.236   moles

step 2: use the mole ratio to determine the   moles of ag

from equation above   cu: ag   is 1: 2

therefore the moles of ag   =0.236   moles   x 2/1 =0.472   moles

step 3: find the mass   of ag

mass = moles x molar mass

from periodic table   the molar mass of ag =107.87 g/mol

mass   = 0.472   moles x 107.87 g/mol = 50.9 g

3.   the   much   silver   collected worth is   1.797 oz

  convert   50.9 g   to oz

that is   1 gram = 0.0353 oz

          50.9 grams =?   oz

by cross multiplication

={(50.9 grams x 0.0353 oz) / 1   gram}   =1.797 oz