Question

A block of mass 100 g slides on a rough horizontal surface. if the speed of the block decreases from 10 m s to 5 m s, find the thermal energy developed during this process.

Answer 1

here,wg is work done by gravity

Answer 2

Answer:

3.75 J

Explanation:

Given:

• m = mass of the block = 100 g = 0.1 kg
• u = initial speed of the block = 10 m/s
• v = final velocity of the block = 5 m/s

Assume:

• $W_n$ = work done by normal force
• $W_g$ = work done by the weight of the block
• $W_f$ = work done by the friction on the block

When the block slides on the rough horizontal surface, three forces act on it that are normal, weight and the kinetic friction. The kinetic friction acts along the horizontal surface but in the direction opposite to the motion of block. Since the normal and the weight acts perpendicular to the displacement of the block, the work done by these forces will be zero.

$\therefore W_n = 0\ and\ W_g = 0$

Now, using the principle of work-energy theorem, the total work done by normal, weight and friction will be equal to the change in kinetic energy of the block.

$\therefore W_n+W_g+W_f = \dfrac{1}{2}m(v^2-u^2)\\\Rightarrow  0+0+W_f = \dfrac{1}{2}\times 0.1(5^2-10^2)\\\Rightarrow W_f = -3.75\ J$

This means negative work is done on the block.

We know that friction force causes heating of the substances. So, the heat is released in this process.

Hence, the thermal energy released during this process is 3.75 J.