Answer:
(D) Va > Vb. The forces between the atoms in a block and the atoms in a surface oppose the motion of the block and are greater on average for block B.
Explanation:
Given that, Two identical blocks, block A and block B, are placed on different horizontal surfaces. Block A is initially at rest on a smooth surface, while block B is initially at rest on a rough surface.
And now, a constant force F₀ is exerted on each block for a time Δt.
Now, speeds of blocks A and B are vA and vB respectively.
In case of block A the surface is smooth, so there is no opposing force.
Whereas as, in case of block B, the surface is rough which means friction opposes the motion
So, some of the applied force is used to overcome this friction which makes the speed of block B vB to be less than that of block A vA.
⇒ Va > Vb.
And completely eliminating friction is not possible.
so, even smooth surface has friction which is very very little.
so, The forces between the atoms in a block and the atoms in a surface oppose the motion of the block and are greater on average for block B.
