Weight word problems

Learn how to calculate the weight when the mass is given with some weight word problems. Also learn how to get the mass when the weight is given.

Question #1:

If a scale says 80 kg after you step on it, is that a measure of your weight?

A common misconception is that a scale always gives you your weight.

When the scale says 80 kg, it is telling you about your mass.

To get your weight, you either need to convert the mass to pounds or Newtons.

Question #2:

If 2 kg of feather weighs 19.6 Newtons, does 2 kg of nails weigh 19.6 Newtons?

Yes, at the earth's surface 2 kg of anything will have the same weight.
Because feathers are much lighter than nails, some may have a tendency to think that it will weigh less. However, once you pack 2 kg of each material, 2 kg is 2 kg and it will weigh the same for both materials.  

Problem  #1:

What is the weight of a baby with a mass of 3 kg?

Solution

To find the weight, use the formula below:

w = m × g

w = 3 kg × 9.8

w = 29.4 Newtons

Problem #2:

You step on the scale and it says 100 kg. You brother steps on the scale and it says 220 pounds. Who is heavier you or your brother?

Solution:

To get your weight, multiply 100 kg by 2.2. ( 1 kg weighs 2.2 pounds)

2.2 multiplied by 100 equals 220.

You and your brother have the same weight.

Weight word problems with a little more math

The weight word problems below are just a little more challenging. They shows how to get the mass from the weight.

Problem #3:

An orange weighs about 1 N. what is the mass of the orange in grams?

(Use g = 10 Newtons instead of 9.8 to simplify the math.)

Solution: 

mass =
weight / g

mass =
1 / 10

m = 0.1 kg

1 kg = 1000 grams

0.1 kg = 1000 × 0.1 = 100 grams

Problem #4:

If your weight is 240 pounds, what is your mass?

What is your mass on the moon?

What is your weight in Newtons ?

How much would you weight on the moon?

Solution:

The mass is expressed in kilograms ( kg ) and 1 kg weighs 2.2 pounds.

Let's us use chain-link conversion  and the concept of conversion factor to solve this problem to find your weight 

 Solution:

1)

The conversion factor is  
1 kg / 2.2 pounds

Multiply the conversion factor by 240 pounds

1 kg / 2.2 pounds
× 240 pounds

This simplify to  
240 kg / 2.2

Your mass is equal to 109.09 kg.

2) Your mass is the same on the moon!

3)

w = m × g

w = 109.09 × 9.8

w = 1069.082 Newtons

4) On the moon, gravity is about one-sixth that of the earth.

Therefore, just get one-sixth of 1069.082 to get your weight on the moon.

One-sixth of 1069.082 is the same as 1069.082 divided by 6.

1069.082 divided by 6  equals 178.18.

Back to definition of inertia or Newton's first law


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