<span>gravitational potential energy : P
Gravity : g
Mass : m
height : h
P = mgh = 3 x 9.8 x 0.45 = 13.23 Joule
Potential energy is work , from the known formula
W = Fd ( work = force x distance )
W = P ( in case of potential energy height change)
F is the force acting on the body in case of ideal ramp , the only force acting is the weight of the body
F = mg ( not just <m> as the force is mg (Newton) gravity effect)
d is the displacement in direction of force, as we have considered the force to be the weight not it's component in direction of the ramp , the change in displacement is the change in height so
d = h
W = Fd = (F = mg) x (d = h) = mgh
W = mgh = P
</span>
angle 2 is congruent to angle six
Eliminate y by writing the bottom equation into the top one:
-1/2x - 4 - 3x = 3
-3.5x = 7
x = -2
y= -1/2 * -2 - 4 = -3
F(x)=-2x+4x-7
f(x)=2x-7
now f(-4)=2(-4)-7=-8-7=-15
So it will be -15