Momentum, Impulse, Work, Power

Harmandip Singh, Nasif Mahmud, Mohammed Yeashin, and Ajla

Dupljak

What is Momentum?

Momentum – a measurement of the tendency of an object to stay in motion. SI Unit: [kg-m/s] Formula: momentum = (mass)(velocity)orp = mv

Momentum continued

- The momentum of a body is proportional to both its mass and velocity. If either one increases the momentum will also increase. - Momentum is a vector quantity whose direction is the same as the object's velocity.

Practice Problem 1

1. If the mass of an object is 5kg, and the velocity is

7m/s, what is the momentum?

Answer

Formula first : p = mv     p = (5kg)(7 m/s)      35 kg-m/s

Problem # 2

2. What is the value of the momentum of a 10 kg ball

running down a bowling alley at a speed of 5 m/s?

Answer

Formula first: p = mv  p = (10 kg)(5 m/s)  50 kg-m/s

Impulse

Impulse- the product of the net force acting on an object and the time during which the force acts. The symbol for impulse is J.SI Unit: [kg-m/s] or [Ns] (Equivalent to momentum)The unit for impulse and the unit for momentum are equivalent. The Impulse is also the change in momentum for an object in motion.

Calculating Impulse

•J= F net(T) = ΔP•(Force)(Time) = Impulse [kg * m/s2]•Δp= mΔv –Δp= m(v’-v)–Δp= mv’-mv –Δp= p’-p

Practice Problem 3

3. A gust of wind exerts a 300. N net force on a 1000.-kg sailboat for 15 s. What is the change in the momentum and velocity of the boat?

Answer

Formulas first : J =Ft, p=mv,J= ΔpJ= (300.N)(15 s)= 4500 J= Δp= 4500kg-m/sp=mvv=p/m= (4500kg-m/s)/(1000.kg)= 4.5m/s

Demonstration

http://www.youtube.com/watch?v=NBaFIiBGjpI

HW: AMSCO pg. 36-37  #153, 162, 170

Work

Work: In physics, work is done whenever a force acts on an object in the direction of the objects motion. If an object is not in motion no work is being done.

 Si Unit: J (Joule)

1J = 1newton · meter = 1N · m

- Work is the product of the magnitude of the applied force F and the objects displacement d in the direction of the force.

-When calculating force only the force parallel to the objects motion can be used.

-Work is a scalar quantity. If an object is not moving no work is being done.

Practicing with Work and Power

1. How much work is done on a downhill skier by an average braking force of 9.8 × 102 Newtons to stop her in a distance of 10. meters?

Solutions   

1. Formula first: W=Fd    W= 9.8 × 102 N ·10.m    W=  9.8 ×103J  

 

   

 

2. What is the work required to raise a 10. - kilogram box from the surface of the earth to a height of 5.0 meters?

 

2. Formulas first: w=mg, W=Fd    w= 10.kg × 9.8 m/s2     w= 98. N    W=Fd    W= 98.N ×5.0m    W= 490J

Power

 Power is the amount of work done per unit time. Like work, it is a scalar quantity. The symbol for power is P.

Power = (work/time)o P=W/t o Since W=Fd, we can write: P= (Fd/t).o Since v= d/t we can write: P= (Fd/t)=Fv.

• Thus, power can also be expressed as the product of the applied force and the velocity of the object

• SI Unit = Watts --> J/Sec 

 

3. If energy is supplied at the rate of 10 watts, how much work is done during 2 seconds?

 

3. Formula first: P=W/t    Pt=W    10watts × 2s= W    20J=W

Work and Power Demonstration

    HW: AMSCO pg. 59-60  #1, 9, 17