Physics 2020 JAMB Past Questions - Question 11: A piece of substance if specific heat capacity 450 J Kg-¹K-¹ falls through a vertical distance of 20m from rest. calculate the rise in temperature of the substance on hitting the ground when all its energies are converted into heat

Correct Answer

B

Explanation

Mgh = mcѳ ; m 10 X 20 = m X 450 X ѳ ѳ = 4/9 oc
To calculate the rise in temperature of the substance when all its energies are converted into heat, we can use the principle of conservation of energy. The potential energy lost by the substance as it falls is converted into heat energy, raising the temperature of the substance.

The potential energy lost by the substance as it falls can be calculated using the formula:

PE = mgh

Where:
PE = potential energy
m = mass of the substance
g = acceleration due to gravity (approximately 9.81 m/s²)
h = height fallen (20 m in this case)

The potential energy lost will be converted into heat energy, and we can use the specific heat capacity (c) of the substance to calculate the rise in temperature (ΔT) using the formula:

PE = mcΔT

Where:
c = specific heat capacity (450 J/kg·K in this case)

First, we need to calculate the potential energy lost by the substance:
PE = mgh
PE = m * 9.81 * 20

Next, we can use the potential energy to calculate the rise in temperature:
PE = mcΔT
m * 9.81 * 20 = m * 450 * ΔT

We can solve for ΔT:
ΔT = (m * 9.81 * 20) / (m * 450)
ΔT = (9.81 * 20) / 450
ΔT ≈ 0.435 K

So, the rise in temperature of the substance on hitting the ground, when all its energies are converted into heat, is approximately 0.435 Kelvin.