The students start rolling their backpacks at the same speed. Which backpack is pulled with a larger force?

 - a backpack carrying 5 pounds
 - a backpack carrying 7 pounds
Look for the backpack that is heavier.
A backpack carrying 7 pounds is heavier than a backpack carrying 5 pounds. So, the backpack carrying 7 pounds needs to be pulled with a larger force to start rolling at the same speed as the other backpack.