Question

A boy throws a ball up into the air with a speed of 8.2 m/s. The ball has a mass of 0.3 kg. How much gravitational potential energy will the ball have at the top of its flight? (Assume there is no air resistance

Answer 1

We can use the law of conservation of energy to solve the problem.

The total mechanical energy of the system at any moment of the motion is:
$E=U+K = mgh + \frac{1}{2}mv^2$
where U is the potential energy and K the kinetic energy.

At the beginning of the motion, the ball starts from the ground so its altitude is h=0 and therefore its potential energy U is zero. So, the mechanical energy is just kinetic energy:
$E_i = K_i = \frac{1}{2}mv^2 = \frac{1}{2}(0.3 kg)(8.2 m/s)^2=10.09 J$

When the ball reaches the maximum altitude of its flight, it starts to go down again, so its speed at that moment is zero: v=0. So, its kinetic energy at the top is zero. So the total mechanical energy is just potential energy:
$E_f = U_f$
But the mechanical energy must be conserved, Ef=Ei, so we have
$U_f = K_i$
and so, the potential energy at the top of the flight is
$U_f = K_i = 10.09 J$

Answer 2

Answer:

10.1 like the other dude answered

Explanation: