Question

A van of mass 1500 kg travelling at a speed of 54km/h is stopped in 10 s . assuming that all the mechanical energy lost appears as thermal energy in the brake mechanism , find the average rate of production of thermal energy in cal/s​

Answer 1

The average rate of production of thermal energy is 4000 cal/s.

Explanation:

Given that,

Mass of van = 1500 kg

Speed = 54 km/h

$v=54\times\dfrac{5}{18}$

$v=15\ m/s$

Time = 10 s

We need to calculate the kinetic energy

Using formula of kinetic energy

$K.E=\dfrac{1}{2}mv^2$

Put the value into the formula

$K.E=\dfrac{1}{2}\times1500\times15^2$

$K.E=168750\ J$

We need to calculate the energy in cal

$K.E=\dfrac{168750}{4.2}$

$K.E=40178.57\ cal$

The loss in total energy of van is

$K.E=40178.57\ cal$

The loss in energy per second

$\Delta K.E=\dfrac{40178.57}{10}$

$\Delta K.E=4017.8\ cal/s$

The average rate is

$\Delta K.E=4000\ cal/s$

Hence, The average rate of production of thermal energy is 4000 cal/s.

Learn more :

Topic : thermal energy

https://brainly.in/question/1584131