A lorry of mass 3000kg traveling to a constant velocity of 72km/h collides with a stationary vehicle of mass 600kg. the impact takes 1.5sec before the two move together at a constant velocity for 15sec . Calculate the change in kinetic energy

Answer 1

First, let's convert the velocity of the lorry from km/h to m/s:
72 km/h = 72 * 1000 / 3600 = 20 m/s

Next, we need to calculate the initial kinetic energy of the lorry:
KE_lorry_initial = 0.5 * mass_lorry * velocity^2
KE_lorry_initial = 0.5 * 3000 * 20^2
KE_lorry_initial = 600000 J

Now, let's calculate the initial kinetic energy of the stationary vehicle:
KE_vehicle_initial = 0.5 * mass_vehicle * 0^2
KE_vehicle_initial = 0 J

The total initial kinetic energy before the collision is:
Total KE_initial = KE_lorry_initial + KE_vehicle_initial
Total KE_initial = 600000 J + 0 J
Total KE_initial = 600000 J

After the collision, the two vehicles move together at a constant velocity. Let's calculate this final velocity:
Let Vf be the final velocity
Vf = distance / time
Vf = 0 / 15
Vf = 0 m/s

Now, let's calculate the final kinetic energy of the system:
KE_final = 0.5 * total_mass * Vf^2
KE_final = 0.5 * (3000 + 600) * 0^2
KE_final = 0 J

The change in kinetic energy is given by:
Change in KE = KE_final - KE_initial
Change in KE = 0 - 600000
Change in KE = -600000 J

Therefore, the change in kinetic energy during the collision is -600,000 Joules.