The echo is heard 2.80 s later, this means this is the time the sound takes to travel to the reflecting object and then back to us. So, during this time, the sound wave has covered the distance L between us and the object twice:

The speed of the sound wave is:

, and since it is moving by uniform motion, we can find the distance covered by the wave using

And we said this corresponds to twice the distance between us and the reflecting object, so:

so, the object is 480 meters away.
Answer:
A pair of oxygen atoms is a molecule of oxygen. A molecule is the smallest particle of a substance that exists independently. Molecules of most elements are made up of only one of atom of that element. Oxygen, along with nitrogen, hydrogen, and chlorine are made up of two atoms.
Explanation:
I can help you with 5. 5 is a displacement-time graph.
At A it is moving in a positive direction and speed is constant.
At B it is stationary or at rest.
At C, movement is negative and it is decreasing or decelerating
At D, it’s a general downwards movement in the negative direction that can be described as overall constant
<u>Answer:</u>
The correct answer option is momentum.
<u>Explanation:</u>
Momentum is the product of an object's mass and velocity.
It is a term which describes the relationship between the mass of an object and the velocity of an object.
Momentum can be represented in the form of an equation as:
P = mv
where P is the momentum,
m is the mass of the object; and v is the velocity of that object.
The jnd for a 100-gram weight, according to Weber's law will be 10 gram.
<h3>What is Weber's law?</h3>
It should be noted that Weber's law asserts that the nature of any given stimulus will always affect how change is perceived. In other words, the size, weight, importance, etc. of the prior situation and the significance of the change both influence whether a change will be observed.
In this case, it was given that the jnd for a 10-gram weight was 1 gram, therefore, the jnd for 100 gram will be;
= 100 / 10
= 10 gram
Therefore, jnd for a 100-gram weight, according to Weber's law will be 10 grams.
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