To find the kinetic energy of the body just before hitting the ground, we need to calculate its kinetic energy at the highest point of its trajectory when its velocity becomes zero. At that point, all its initial kinetic energy is converted into potential energy, and as it falls back to the ground, this potential energy is converted back into kinetic energy.
The kinetic energy (KE) of an object is given by the equation:
KE = (1/2) * m * v^2
where: m = mass of the body (4 kg) v = velocity of the body
Initially, the body is thrown vertically upward with a velocity of 5 m/s. When it reaches the highest point, its velocity becomes zero before it starts falling back down.
Therefore, to calculate the kinetic energy just before hitting the ground, we need to determine the velocity of the body when it reaches the ground. Since the velocity at the highest point is 0 m/s, the velocity just before hitting the ground will be the same magnitude but in the opposite direction, i.e., -5 m/s.
Substituting the values into the kinetic energy equation:
KE = (1/2) * 4 kg * (-5 m/s)^2 = (1/2) * 4 kg * 25 m^2/s^2 = 50 J
Hence, the kinetic energy of the 4 kg body just before hitting the ground is 50 Joules.