<span>A. A girl hits a volleyball. Her hand exerts a force on the ball, and the ball exerts a force on her han</span>
If you are cold and you rub your hands together then that friction can create warmth. Useful
If you're sliding down a staircase railing and your hands are on the raiking then the friction may burn your hands a little. Not useful<span />
Kinetic energy of the horse and rider = 1/2 (mass) (speed)²
At 4.0 m/s : KE = 1/2 (55kg) (4 m/s)² = 440 joules
At 6.0 m/s : KE = 1/2 (55kg) (6 m/s)² = 990 joules
She increased the kinetic energy of herself and her vehicle by 550 joules,
so she must have put at least that much work into it.