In winter, the Neva is covered with ice, the layer thickness of which is 60 cm. How many wagons of coal

In winter, the Neva is covered with ice, the layer thickness of which is 60 cm. How many wagons of coal will it take to melt this ice? Take the average width of the river equal to 300 m, length – 65 km. The car has a capacity of 50 tons of coal. Where does heat come from when ice melts under natural conditions?

h = 60 cm = 0.6 m.

a = 300 m.

l = 65 km = 65000 m.

ρl = 916 kg / m ^ 3.

λ = 3.4 * 10 ^ 5 J / kg.

k = 2.7 * 10 ^ 7 J / kg.

m1 = 50 t = 50 * 10 ^ 3 kg.

n -?

Let us find the amount of heat Ql, which is necessary for melting ice according to the formula: Ql = λ * ml, where λ is the specific heat of melting of ice, ml is the mass of ice.

ml = Vl * ρl = h * a * l * ρl.

Ql = λ * h * a * l * ρl.

Let us find the amount of heat Qу, which is released during the combustion of 1 car of coal: Q1 = k * m1, where k is the specific heat of combustion of coal, m1 is the mass of 1 car with coal.

The number of cars with coal n is found by the formula: n = Ql / Q1 = λ * h * a * l * ρl / k * m1.

n = 3.4 * 10 ^ 5 J / kg * 0.6 m * 300 m * 65000 m * 916 kg / m ^ 3 / 2.7 * 10 ^ 7 J / kg * 50 * 10 ^ 3 kg = 2699 …

In spring, the ice will melt due to the thermal energy of the environment.

Answer: to melt ice, you need n = 2699 cars with coal.