Unit 8 Notes Momentum

p=mv In the last unit, we learned about conservation of energy. In this unit, we see conservation of momentum Momentum (p) is equal to mass times velocity *** P is for power. p is for momentum***

Impulse F = ma F = m(∆v) /(∆t) F∆t = m(∆v) J = ∆p J stands for impulse This is the change in momentum. It is also the area underneath a force vs time graph. If mass is constant, ∆p = m∆v = m(v f –v 0 ) A lot of times, we can even say F∆t = m(v f –v 0 )

Example: A 20kg block is at rest. A 5N force is applied to it for 3s. a)Solve for the impulse. J= F∆t = (5N)(3s) = 15Ns b)Solve for the block’s velocity at the end of the 3 seconds. ∆p = J = m(v f –v 0 ) 15Ns = 20kg(v f –0)v f =0.75m/s

Momentum, like energy, can’t be created or destroyed. Momentum is directly transferred from one object to another. Unlike energy, momentum cannot be dissipated. ∑p = ∑mv = constant ∆p 1 = -∆p 2 In words: when one object gains momentum, another object loses the same amount of momentum.

Example Bobby runs his 2000kg car into a 5000kg parked car at 20m/s. The cars bounce off each other such that Bobby’s car stops completely, what is the new velocity of the car he hit immediately after the crash? m 1 v 1 + m 2 v 2 = m 1 v 1 + m 2 v 2 (2000kg)(20m/s) + (5000kg)0 = (2000kg)0 + (5000kg)v 40,000(kg*m/s) = (5000kg)v v = 8m/s

Types of Collisions Elastic Collision: When two objects bounce off each other. m 1 v 1 + m 2 v 2 = m 1 v 1 + m 2 v 2 Perfectly elastic collision: No kinetic energy is lost during the collision. Really bouncy objects can come close to this.

Inelastic collision: A lot of kinetic energy is lost during the collision. Two objects combining together and moving away at a common velocity. m 1 v 1 + m 2 v 2 = (m 1 + m 2 ) v combined

Explosion: Two objects move apart due to some sort of energy being converted to kinetic energy. (m 1 + m 2 )v i = m 1 v 1 + m 2 v 2