Answer:
a) 80 J
Explanation:
The gravitational potential energy of the ball relative to the ground is:
[tex]U=mgh[/tex]
where
m = 2 kg is the mass of the ball
g = 9.8 m/s^2 is the acceleration due to gravity
h = 4 m is the heigth of the ball above the ground
Substituting numbers into the equation,
[tex]U=(2 kg)(9.8 m/s^2)(4 m)=78.4 J \sim 80 J[/tex]
So the correct answer is
a) 80 J
