momentum, impulse, work, power harmandip singh, nasif mahmud, mohammed yeashin, and ajla dupljak
TRANSCRIPT
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?
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?
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?
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?
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