<h2>
Answer: an underground lake</h2>
Explanation:
In general, sound (mechanical waves) travels faster in solids than in liquids, and faster in liquids than in gases. This is because <u>the speed of the mechanical waves is determined by a relationship between the elastic properties of the medium </u>in which they are propagated and the mass per unit volume of the medium (that is:<u>density</u>).
In other words: The speed of sound varies depending on the medium through which the sound waves travel.
So, if we are told the sound wave initially had a speed of 4,000 m/s and it suddenly decreases to 1,500 m/s, this means the sound waves passed from a solid medium to a liquid medium.
Hence, the correct option is: an underground lake.
A beam of laser is directed at a reflecting surface put on the moon when the beam of laser is reflected a receiver on the each measure the time since the beam was sent till it was received. Laser is simply light so it has constant velocity in vacuum ~ air (c = 3 x 10^8 m/s)
to find the distance:
t : time measured between launching the beam and receiving it
d : distance
d = ct
Mantle convection
Explanation:
The driver of moving plates is the mantle convection.
Convection is a heat transfer process that involves the movement of fluids from one place to another.
How does convection occur in the mantle?
- Part of the mantle known as the asthenosphere is a hot liquid. It moves slowly and does not readily flow.
- Over riding the asthenosphere is the brittle lithosphere made up of the upper mantle and the entirety of the crust.
- The asthenosphere is at a higher temperature compared to the lithosphere on top.
- In order to achieve stability and thermal equilibrium, the asthenosphere rises to the surface whereas the dense and cold lithosphere sinks down.
- This way a convective cell is set up.
- Hot materials rises to the surface because they are light whereas cold materials on the surface sinks into the asthenosphere.
- Through this the plates moves.
Learn more:
Mantle brainly.com/question/9582362
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Answer:
The initial speed of the bullet is 
.
Explanation:
The collision between bullet and block is inelastic and let suppose that motion occurs on a horizontal surface, so that changes in gravitational potential energy can be neglected. Initially, the intial speed of the bullet-block system can be determined with the help of the Work-Energy Theorem and the Principle of Energy Conservation:
The initial speed of the bullet-block system is:
Now, the initial speed of the bullet is determined by applying the Principle of Momentum Conservation:
B damage the protective layers of the artery walls, which can intimately lead to heart disease.
