Question

Two balls of equal size are dropped from the same height from the roof of a building. the mass of ball a is twice that of ball b, m subscript a equals 2 m subscript

b. when the two balls reach the ground, how do their kinetic energies compare?

Answer 1

The mass of ball a is twice the mass of ball b:
$m_a = 2 m_b$
This means that the initial potential energy of ball a ($U_a = m_a gh=2 m_b gh$) is twice the potential energy of ball b ($U_b = m_b g h$):
$U_a = 2 U_b$
When the two balls reach the ground, the potential energy of each ball has converted into kinetic energy (since now their altitude is h=0), because the total mechanical energy of each ball must be  conserved. Therefore:
$K_a = U_a$
$K_b = U_b$
and so the kinetic energy of ball a must be twice the kinetic energy of ball b:
$K_a = 2 K_b$

Answer 2

Answer:

5.5 m/s

Explanation: