Physics · Laws Of Motion · NEET
No, but they are linked. Momentum p = mv is a property a moving body already has. Impulse J is what you give to a body to change its momentum. The impulse-momentum theorem says the impulse you apply equals the change in momentum: J = mv - mu. They share the same SI unit (kg m/s = N s), which is why students mix them up. Rule: momentum is 'how much motion is there now', impulse is 'how much motion was added or removed'.
Impulse has two equal units: newton-second (N s) from J = F x t, and kilogram-metre-per-second (kg m/s) from J = change in momentum. They are the same because 1 N = 1 kg m/s^2, so 1 N s = 1 kg m/s^2 x s = 1 kg m/s. In NEET a question may give options in either form - both are correct for impulse.
Use whichever the data gives you. If the question gives a force and a contact time, use J = F x t (average force). If it gives masses and velocities before and after, use J = mv - mu = change in momentum. Both give the same impulse because the impulse-momentum theorem makes them equal. For a ball that reverses direction, remember mv - mu becomes m(v) - m(-u), so signs matter.
Impulse is a vector because it equals the change in momentum, and momentum is a vector. Its direction is the direction of the momentum change (final momentum minus initial momentum), which is also the direction of the average force. When a ball bounces straight back, the impulse points opposite to the incoming ball, away from the wall or ground.
Because the velocity reverses direction. Take downward as negative and upward as positive. Initial momentum = -m(u_down), final momentum = +m(v_up). Change = m(v_up) - (-m(u_down)) = m(v_up + u_down). The two speeds add because the direction flips. This is the single most common trap in impulse rebound problems.
A ball of mass 0.15 kg is dropped from a height of 10 m, strikes the ground and rebounds to the same height. The magnitude of the impulse imparted to the ball is nearly (g = 10 m/s^2):
A ball of mass 0.5 kg is dropped from a height of 40 m. It hits the ground and rebounds to a height of 10 m. The impulse imparted to the ball during its collision with the ground is (g = 9.8 m/s^2):
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Impulse is force multiplied by the time it acts (J = F x t), and it equals the change in momentum of the body.
It states that the impulse applied to a body equals its change in momentum: F x t = mv - mu. It comes directly from Newton's second law F = change in momentum / time.
Impulse is a vector. Its direction is the same as the change in momentum and the same as the average applied force.
The dimensional formula of impulse is [M L T^-1], the same as momentum, since impulse equals change in momentum.
An impulsive force is a very large force that acts for a very short time and produces a finite change in momentum, like a bat hitting a ball or a wall reflecting a ball.
