Question

A block is given an initial push along a rough horizontal fixed table surface and after some time it stops due to friction. For the system of block and table
A. temperature increase
B. heat supplied is positive
C. heat supplied is negative
D. total energy decreases

Answer 1

Hint: Think about the force acting due to a rough surface. Remember that it is asked about the system of both the table and block not individually of any one. Think about the energy terms involved in it.

Complete answer:
When an object moves along a rough horizontal surface, it experiences frictional force. Friction is not a conservative force. Hence the individual energy is not constant for the block only or the table. However for the total system, the energy must always remain constant.

Now friction opposes the motion of the object, hence it produces retardation. Due to this the temperature of the system of block and table increases.The temperature increases only due to friction acting between the block and the table. There is no external heat supplied or extracted. If heat is given to the system heat supplied is positive. If heat is taken out, heat supplied is negative. Here the heat supplied is zero.

Hence the correct option is B.

Note:Students should know about the thermodynamic terms of motion. Students should note that the energy of the system will never change. It will be constant. However the energy of the block will not remain constant as there is loss due to friction.