Question

A student drops a 1.5 kg rock off of a 4.0 m tall bridge. The speed of the rock just before it hits the water below is 6 m/s. How much energy was lost due to air resistance?

Answer 1

Answer:

Energy due to air resistance = 31.8 Joules

Explanation:

According to the law of conservation of energy, energy can neither be created nor destroyed but can be transformed from one form to another

Kinetic Energy + Energy due to air resistance = Potential energy..........(1)

If there is no energy loss due to air resistance, potential energy = kinetic energy

mass, m = 1.5 kg

height, h = 4.0 m

speed, v = 6 m/s

Kinetic energy = 0.5 mv²

Kinetic energy = 0.5 * 1.5 * 6²

Kinetic energy = 27 Joules

Potential Energy = mgh

Potential energy = 1.5 * 9.8 * 4

Potential energy = 58.8 Joules

From equation (1)

27 + Energy due to air resistance = 58.8

Energy due to air resistance = 58.8 - 27

Energy due to air resistance = 31.8 Joules

Answer 2

Answer:

Explanation:

Note:

Air resistance in the way means not all of the potential energy can be converted to kinetic energy.

Given:

Mass = 1.5 kg

D = 4 m

Vf = 6 m/s

Energy + KE = PE

= (M × g × d) - (1/2 × M × V^2)

= (1.5 × 9.8 × 4) - (1/2 × 1.5 × 6^2)

= 58.8 - 27

= 31.8 J