The rate of change of linear momentum of a body is directly proportional to the external force applied on it, and takes place always

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The rate of change of linear momentum of a body is directly proportional to the external force applied on it, and takes place always in the direction of force applied.

1. Name this law.

2. Using this law obtain the expression for force.

3. The motion of a particle of mass m is described by y = ut + $\frac{1}{2}$gt2. Find the force acting on it.

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1. Newton’s Second Law.

2. Consider a body of mass ‘m’ moving with a momentum p. Let F be the force acting on it for time internal ∆t. Due to this force the momentum is changed from p to p + ∆p. Then according to Newtons second law, we can write.

Where K is a constant pf proportionality. When we take the limit ∆t → 0, we can write

3.

Hence force F = mg.