1. Define
2. angle of friction
3. angle of repose
4. explain why
5. a horse can not pull a cart and run in empty space
6. it is easier to pull a lawn roller than to push it

Angle of friction is a way to measure the friction between two surfaces. One body in placed on another body (surface) and one of the bodies (usually the flat surface) is made to incline with respect to ground letting gravity work over the first body (placed over the flat surface i.e., over the second body) then the maximum angle of inclination at which the firstbody may remain stable is measured , that angle is called angle of friction and the tangent of that angle is called called coefficient of friction.
 
The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. At this angle, the material on the slope face is on the verge of sliding. The angle of repose can range from 0° to 90°.

Dear Dinesh
 
Please ask one questuon in one thread.
It is easier to pull a lawn roller than to push it.
Explanation:  The force applied to move a body depends upon effective force applied on it including its weight. As effective weight in the case of pulling is less than in the pushing, less force is required in pulling. Hence, it is easier to pull than to push.
In case of  pulling, effective weight of lawn mover = mg-f sin θ
In case of  pushing, effective weight = mg+ f sin θ

A horse cabca pull a cart and run in empty space.
Explanation:When a horse is trying to pull a cart, he pushes the ground backward at an angle from the horizontal. According to Newton’s third law of motion, the ground also apply equal reaction force on the feet of the horse in opposite direction. The vertical component of reaction balances the weight of the horse and horizontal component is responsible for motion of the cart. In empty space, there is no reaction force, therefore a horse cannot pull a cart.