# Physics doubts from Class XI student

1. How to check the correctness of equation s=u+0.5a(2n-1) using dimensional analysis?(Please describe)
2. In law of conservation of linear momentum derivation,why force acting on body B by A is taken as product of mass and acceleration of "B" and not "A" instead of "B"?

Answer

1. The accuracy is checked as usual, but remember that the quantity on LHS is not displacement, but displacement in one second which should have the dimension same as speed or velocity. It can be shown that each of the term on RHS has the dimensions LT-1
2. The force acting on B will be the product of mass of B and the acceleration of B, as force exerted by A is the cause which produced the acceleration. Acceleration of B is caused by the force exerted by A. The acceleration produced in B is directly proportional to the force exerted on it and inversely proportional to the mass of its own (B’s) mass.

Therefore, Force exerted by A on B is equal to the mass of B x acceleration of B