Apaper airplane with mass 0.1 kg is flying 1.5 m above the ground with a speed of 2 m/s. what is the total mechanical energy of the paper airplane?

Total mechanical energy = kinetic energy + potential energy
E = KE + PE
E = ½mv² + mgh
E = ½(0.1 kg)(2 m/s)² + (0.1 kg)(9.8 m/s²)(1.5 m)
E = 0.2 J + 1.47 J
E = 1.67 J

We know that:
EM=Epg+Ek
So:
Epg=mgh
Epg=0,1kg*9,8m/s²*1,5m
Epg=1,47J
Now:
Ek=1/2mv²
Ek=1/2(0,1kg)(2m/s)²
Ek=0,2J
That give us:
EM=1,47J*0,2J
EM=1,67J

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.