Answer with Explanation:
We are given that
A=3i-3j m
B=i-4 j m
C=-2i+5j m
a.


Compare with the vector r=xi+yj
We get x=2 and y=-2
Magnitude=
units
By using the formula 
Direction:
By using the formula
Direction of D:
b.E=-A-B+C


units
Direction of E=
The potential energy is converted into kinetic energy. Hope this helps!
Explanation:
Given that,
Initial speed of the billiard ball 1, u = 30i cm/s
Initial speed of another billiard ball 2, u' = 40j cm/s
After the collision,
Final speed of first ball, v = 50 cm/s
Final speed of second ball, v' = 0 (as it stops)
Let us consider that both balls have same mass i.e. m
Initial kinetic energy of the system is :

Final kinetic energy of the system is :

The change in kinetic energy of the system is equal to the difference of final and initial kinetic energy as :
So, the change in kinetic energy of the system as a result of the collision is equal to 0.
Answer:
When we see a region of a planet that is not as heavily cratered as other regions, it means that the surface of that region is younger.
Explanation:
There are a number of processes that affect planetary surfaces like erosion, volcanism, plate tectonics and the amount of craters by impact of meteorites.
The density of craters in a given region suggests the age of the surface. If the surface is saturated by craters then is likely very old because a long time should have passed for the planet to be hit by so many meteorites. If there are very few craters this may indicate that the surface is quite young, because the other processes described above wouldn't have had enough time to erase them. In any case we need to study the change of the cratering rate over time to determine the age of a given surface.