Question

Mandy works construction. She knows that a 5 meter long metal bar has a mass of 40 kg . Mandy wants to figure out the mass (w) of a bar made out of the same metal that is 3 meters long and the same thickness. What is the mass of the shorter bar?

Answer 1

If you take the weight and divide it by the length, you get the weight-per-meter. So, 40(kg) divided by 5(meters) gives you 8 kilograms per meter. Then to find the weight of the shorter bar, you'd multiply it's length by the number you just found. In conclusion, the shorter bar weighs 24kg.

Answer 2

24 kg

Explanation:

The mass of the unknown bar is represented by the variable w.

We can use a proportion for this problem. We will compare the mass of each bar to its length. The first bar has a mass of 40 kg and a length of 5 m; this gives us the ratio

40/5.

The second bar has an unknown mass and a length of 3 m; this gives us the ratio

w/3

This gives us the proportion

40/5 = w/3

To solve, cross multiply:

40(3) = w(5)

120 = 5w

Divide both sides by 5:

120/5 = 5w/5

24 = w

The second bar has a mass of 24 kg.