Name(s) ______________________________________________________ Hr. _____
Physics, Unit 6, MORE Calculating Weight
Calculating Weight is a very important concept in physics. In our country, forces (including weight) is
measured in pounds (lbs.). However, in the metric system, forces are measured in a unit called the
NEWTON (N). We need to be able to go back and force between the metric system and our system.
Weight (in Newtons) is a product of the mass of the object (in kilograms) times the acceleration due to
gravity (9.8 m/s/s on the Earth). The weight vector is always directed downward.
W = m∙g
Helpful conversions and equations:
 1000 grams = 1 kilogram
 4.45 N = 1 lb (pound)
 2.2 lbs = 1 kg (YOU CAN ONLY use this conversion on the Earth!)
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1. Astronauts sent to the moon were around 700-800 or so Newtons. For example,
Neil Armstrong weighed around 760 Newtons on the Earth.
(a)
What is his weight in pounds (on the Earth)?
(b)
What was Armstrong’s mass in kilograms (on the Earth?)
(c) If the gravity on the Moon is 1.6 m/s/s, what is his weight on the Moon (in Newtons)?
(d) What was Armstrong’s mass in kilograms (on the moon?)
(e) What was Armstrong’s weight on the moon in pounds (hint: you can use a ratio)?
(answers: Depending upon rounding your answers may be slightly different. Neil weighed around 170.8 lbs on the Earth. His mass is
around 77.55 kg. On the moon, he weighs about 124.1 Newtons. His mass on the moon is also 77.55 kg. Remember that mass doesn’t
change when we travel to other planets; weight changes because each planet has a different amount of gravity (little g). He weighs about
28 lbs on the Earth).
More practice with weight, p. 1
2. Over the last few decades, the Russians (Soviets) sent 14 or so satellites to land on
Venus, the planet next to us inward. One was called Venera 16. It had a mass of
4000 kg. Venus has a gravity 8.9 m/s/s.
(a)
In terms of Newtons, how
much heavier was the satellite on the Earth
than on the surface of Venus?
(b) How many pounds did it weigh on the Earth?
(answers: The spacecraft weighs more on the Earth by about 3600 Newtons than on Venus. Why? Earth has more gravity. It weighed
about 39,200 Newtons or 8809 lbs on the Earth.)
3. One honey crisp apple might weigh 0.75 lbs
(a) What is its mass in kilograms?
(b) What is its mass in grams?
(c) What would the apple weigh in Newtons?
(d) What would be its mass in kilograms on Venus? What about the moon?
(answers: The mass of the apple is around 0.34 kg or 340 grams. It would weigh around 3.3375 Newtons. Its mass would be the same on any planet as the
mass doesn’t change. Mass is based on atoms and molecules in the object.)
More practice with weight, p. 2