The force of gravity pulling down on the barbell is 756 newtons (N) How many
newtons of force are exerted by the
weightlifter to hold the barbell up?

Explanation:

The same. The force down (the weight of the barbells) is counter balanced by the weight up ( a person holding the barbells). A little later on, you are going to draw force diagrams showing that these two forces are drawn acting in opposite directions.

You can satisfy yourself by drawing a box and putting 1 arrow pointing up on the bottom and labeling it 756 up and another arrow on the top of the box pointing down and labeling it 756. They balance.

3 1/4 %

explanation:

answer : one can design an experiment using a liquid and an additive that can be added to the liquid and observe the chemical changes in the reaction species.

one would need a beaker which is filled with a known amount of the liquid in which thermometer is placed to measure the temperature changes; after addition of the additive to the liquid solution one can note down the temperature change and find whether the reaction is endothermic or exothermic in nature. by subtracting the initial temperature value with the final temperature one can find the temperature changes.

various combinations of liquid and additive can be used. liquid in this case can be a known quantity of water and additives can be epsom salt or without epsom salt the experiment can be conducted to notice the changes. water and ice, hydrogen peroxide and dry yeast, vinegar and baking soda,etc.