Hannah just finished building a house of cards that stands four stories high. she is worried that it will fall down. which of the following statements must be true?
if no unbalanced force acts upon the house of cards, then it will remain standing forever.
as long as nobody touches the house of cards, it will remain standing.
if hannah adds another card to the house of cards, then it will fall down.
a house of cards is too fragile and must fall down eventually due to gravity.

If no unbalanced force acts upon the house of cards, then it will remain standing forever.

Explanation:

From Newton's first law we understand that for an object to change its state of rest or motion, an external unbalanced force must act on it.

In the given situation, the house of cards is at rest and would remain at rest until and unless an unbalanced external force acts on it. Thus, till then it would remain standing still.

a.) travels faster in solids because the particles are closer together.

air is a gas water is a liquid

the best answer for these questions would be:

1.            c. is smaller

2.            d) concrete operational

3.            b) interaction with the environment – the children interact with their environment can them learn more.

4.            a) parents who reason openly with children can limit a child’s cognitive ability.