Question

A 750 kg National Geographic Drone is rising vertically up into the atmosphere at constant speed. The lift force pushing it upward is 125% of its weight. The drone reaches the cruising speed almost immediately. It takes 25 seconds for the drone to reach a height of 250m starting from the surface.
a. What is the mechanical energy of the drone at the surface?
b. What is the mechanical energy of the drone at the 150 m height?
c. Is the mechanical energy of the drone conserved, increased, or decreased. Explain your choice.
d. What is the work done by each force acting on the drone?

Answer 1

Answer:

a. 0

b. 1.103625 MJ

c. Conserved

d. 1.103625/n MJ where n = The number of forces

Explanation:

The mass of the drone, m = 750 kg

The upward lift force = 125% of the weight of the drone

The time it takes the drone to reach a height of 250 m = 25 seconds

a. The mechanical energy = The kinetic energy + Potential energy

Therefore, given that the drone stars motion from the surface and was initially at rest, the mechanical energy at the surface = 0

b. The mechanical energy at height, h = 150 m, ME₁₅₀ = The potential energy gained = m·g·h

Where;

g = The acceleration due to gravity = 9.81 m/s²

∴ ME₁₅₀ = 750 kg × 9.81 m/s² × 150 m = 1103625 J = 1.103625 MJ

c. The mechanical energy is equivalent to the potential energy of the drone at the 150 m height, therefore, it is conserved

d. The work done by the force = The energy gained

Therefore, where there are n number of forces, the work done by each force = 1.103625/n MJ