Physics Questions

It is to overcome this opposite frictional force , that  we have to apply the needed force to make the body move

Processes that require or give off heat will be limited to changes of state, known as phase changes, and changes in chemical constitution, or chemical reactions. Changes of state involve a solid melting, a liquid freezing, a liquid boiling or a gas condensing.

An exothermic process is one that gives off heat, which is transferred to the surroundings. An endothermic process is a reaction which heat has to be supplied to the system from the surroundings.

Here in all the given options, heat is taken away from them to change there phase. 

Liquid to Solid --- Freezing

Gas to Liquid --- Condensation

Gas to Solid --- Deposition 

are all examples of exothermic processes.

The usual cause of sea breeze is the difference in specific heat capacity between land and water Land heats and cools more quickly than water.

What is the cause of a sea breeze?

The air over the land is warmed and rises, to a greater temperature than that over the sea. This produces a convection current, with cooler air flowing in from over the sea to replace that rising from the land. At night the land cools more than the sea, so the action reverses to produce a land-breeze, blowing off the land.

without this centripetal force, circular motion is not possible. It acts radially towards the centre and if this force is removed there will be no circular motion but the revolving body will fly off at a tangent.

Black  surfaces are good emitters of heat ( They are also good absorbers of heat). If the black surface is rough too, the emitting will be better. So (b) is the correct answer. Shining surfaces reflect back radiation. So if the black surface is also shining the effectiveness of emitting heat is lessened.

Blood is a heterogeneous mixture because the blood cells are physically separate from the blood plasma. The cells have different properties than the plasma. The cells can be separated from the plasma by centrifuging, which is a physical change.