Work = force x distance. In units, Joules = Newtons x meters.
So: Work = 50 Newtons x 3 meters
Work = 150 joules. Answer D is correct
FYI - to ace physics, you should learn to identify these values using their fundamental units:
Force = Newtons = Kg·m/s²
Work = joules = kg·m²/s²
Power = watts = kg·m²/s³
In high school physics, If you learn to arrange equations so the units work out properly for the answer, you'll get most problems correct.
When you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. This increases the space in your chest cavity, into which your lungs expand. The intercostal muscles between your ribs also help enlarge the chest cavity. They contract to pull your rib cage both upward and outward when you inhale.
If it produces 20J of light energy in a second, then that 20J is the 10% of the supply that becomes useful output.
20 J/s = 10% of Supply
20 J/s = (0.1) x (Supply)
Divide each side by 0.1:
Supply = (20 J/s) / (0.1)
<em>Supply = 200 J/s </em>(200 watts)
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Here's something to think about: What could you do to make the lamp more efficient ? Answer: Use it for a heater !
If you use it for a heater, then the HEAT is the 'useful' part, and the light is the part that you really don't care about. Suddenly ... bada-boom ... the lamp is 90% efficient !