Hollis hangs a fish from a digital force meter in the lab. The display reads 49 N.
The meter gives the fish's weight: 49 N. What is the fish's mass, in kilograms?
The equation w = mg holds three quantities. Given any two of them, the third can be found.
This time the unknown is not w. The unknown is m.
So rearrange the equation to make the unknown the subject.
Start from w = mg. Divide both sides by g, and m stands alone: m = w ÷ g.
The same move works when g is the unknown. Divide both sides by m: g = w ÷ m.
The routine gains one step. Write down the values, decide which quantity is unknown, make it the subject, then substitute and calculate.
The result line carries the unknown's own unit: kilograms for a mass, N/kg for a field strength.
A fish hangs from a force meter that reads 49 N on Earth. Take g = 9.8 N/kg. Calculate the fish's mass.
Write down the values:
w = 49 N, g = 9.8 N/kg, m = ?
Write down the equation:
w = mg
Make m the subject:
m = w ÷ g
Substitute in the values, and calculate:
m = 49 ÷ 9.8 = 5.0
The fish's mass is 5.0 kg.
On the Moon, a 6.0 kg rock weighs 9.6 N. Calculate g on the Moon.
Write down the values:
w = 9.6 N, m = 6.0 kg, g = ?
Write down the equation:
w = mg
Make g the subject:
g = w ÷ m
Substitute in the values, and calculate:
g = 9.6 ÷ 6.0 = 1.6
g on the Moon is 1.6 N/kg.
A sack of cement weighs 196 N on Earth. Take g = 9.8 N/kg. Enter its mass in kg.
A table lamp weighs 24.5 N on Earth. Take g = 9.8 N/kg. Enter its mass in kg.
On one planet, a 50 kg probe weighs 185 N. Enter g there in N/kg.
A wrestler weighs 686 N on Earth. Take g = 9.8 N/kg. Enter his mass in kg.
A 4.0 kg rock weighs 35.2 N on another planet. Enter g there in N/kg.
On the Moon, g = 1.6 N/kg. A crate of lander parts weighs 128 N there. Enter its mass in kg.
A loaded backpack weighs 73.5 N on Earth. Take g = 9.8 N/kg. Enter its mass in kg.
Demi's 25 kg supply crate lands on one of Jupiter's moons and weighs 35 N there. Enter g on that moon in N/kg.
Hollis knows a crate's weight w and the local field strength g. Which calculation gives the crate's mass?