So they stay together but can open to allow boats through.
Answer: D
Explanation:
Forces can be divided into those that act by direct contact—such as when you push on a door to open it—and those that act at a distance, where there is no apparent physical contact between the objects. Magnetism, and electrical charge, and gravitation are examples of forces that act at a distance.
A) ice wedging
The “water freezing” part should help you get the right answer.
I think the answer is:
B. Chemical Change.
The answer is 6×10⁹ years.
K-Ar dating is radioactive dating method used to measure a time elapsed since the rock is cool enough to trap Ar after a radioactive decay of 40K to 40Ar. It can be expressed as:
where:
- elapsed time
- half-life of K40
- amount of K40
<span>
- amount of Ar40
</span>
We know that a half-life of K40 is 1.251<span>×10⁹ years:
</span>
We do not know absolute value of amount of K40 and Ar40, but we know percentage and can express them as following:
<span>
</span>
So:
⇒ t = <span>6×10⁹
</span>
Thus, the rock is old <span>6×10⁹ years.</span>