Answer: 
Explanation:
Given
The velocities of the protons are 400 m/s and 450 m/s
Mass of the Proton is 
Since they travel in the opposite direction, therefore, their momentum cancels out each other.
Momentum is the product of mass and velocity

The direction of momentum is in the direction of proton having 450 m/s velocity.
because they are floating on top of the liquid mantle.
Answer:
Explanation:
The rocky planets include Mercury, Venus, Earth, and Mars. they are made up of rocks and metals and have solid surfaces.They are the closest four planets to the Sun. The gas giants are Neptune, Uranus, Saturn, and Jupiter. they are further from the sun and are in the outer part of the solar system. I hope this helps!
The answers are:
a) 
b) 
Why?
It seems that you forgot to write the questions of the problem, however, in order to help you, I will try to complete it.
The questions are:
a) How much work does the heart do in a day?
b) What is its power output in watts?
So, solving we have:
We need to convert from liter to cubic meters in order to use the given information, so:

Also, we need to find the mass given the density of the blood.

Now, calculating how much work does the heart do in a day, we have:

Then, calculating what is the power output and its horsepower, we have:

Have a nice day!