Hi! ;D
the slope of the line tells us the rate of change of y relative to x. If the slope is 2, then y is changing twice as fast as x; if the slope is 1/2, then y is changing half as fast as x, and so on. ... In other words, if the line is near vertical then y is changing very fast relative to x.
Assuming conservation of energy:
Energy before = 7000 + 4000 = 11 000 MJ
Energy after = 2000 + Kinetic = 11 000
Therefore Kinetic = 11 000 - 2 000
Kinetic = 9 000 MJ
It is symbols to make it easier and to save space!
