Impulse and Momentum

Terminology

Impulse: FΔt, or the product of the average force on object and the time interval over which it acts (measures in Newton-seconds)

Momentum: mv, or the product of the object’s mass and the objects velocity

Impulse-momentum Theorem: FΔt= pf –pi ; The impulse on an object is equal to the object’s final momentum mines the object’s initial momentum (p= momentum)

Concepts

The momentum of an object is the product of its mass and velocity and is a vector quantitiy.

The impulse of an object is the average net force exerts on the object multiplied by the time interval over which the force acts.

The impulse on an object is equal to the change in momentum of the object.

Questions

A pitcher claims he can throw a 0.151 kg baseball with as much momentum as a 3.0 g bullet moving with a speed of 1.50  103 m/s. Which of the following is true a) ball has greater kinetic energy. b) both have the same kinetic energy.     c) the bullet has greater kinetic energy. None of the above

A pitcher throws a 0.15 kg baseball so that it crosses home plate horizontally with a speed of 10 m/s. It is hit straight back at the pitcher with a final speed of 24 m/s. Assume the direction of the initial motion of the baseball to be positive. What is the impulse delivered to the ball? Find the average force exerted by the bat on the ball if the two

are in contact for 2.0  10-3 s.

Equations

F=MAF=M (ΔV/ ΔT)P=MVFΔt= MΔV

P= momentumV=veolicityM= massF= forceT= time

Conservation of Linear Momentum in Collisions

Terminology

Closed system: a system that does not gain or lose mass

Isolated system: a closed system on which the net external force is zero

Law of conservation of momentum: states that the momentum of any closed, isolated system does not change

Concepts and Equations

In a linear collision, momentum is neither gained nor loss. Momentum is transferred to another object.

½m1iv1i² + ½m2iv2i²= ½m1fv1f² + ½m2fv2f²

m1v1i + m2v2i= m1v1f + m2v2f

m1v1i + m2iv2i= vf (m1+ m2)

Quesions

A 1245 kg car traveling initially with a speed of 25.0 m/s in an easterly direction crashes into the rear end of a 9100 kg truck moving in the same direction at 20.0 m/s. The velocity of the car right after the collision is 18.0 m/s to the east. What is the velocity of the truck right after the collision?

In a football game, a receiver is standing still, having just caught a pass. Before he can move, a tackler, running at a velocity of +4.8 m/s, grabs him. The tackler holds onto the receiver, and the two move off together with a velocity of +2.6 m/s. The mass of the tackler is 116 kg. Assuming that momentum is conserved, find the mass of the receiver.  A) 121 kg B)107 kg C) 73 kg D) 98 kg