Download Chapter 11: Forces

Bellringer 9/30
• A skier leaves the horizontal end of a ramp
with a velocity of 25.0m/s East and lands
70.0 m from the base of the ramp. How
high is the end of the ramp from the
ground?
Chapter 6: Momentum and Collisions
• Momentum – the product of the mass
and velocity of an object
Linear Momentum (p):
p=mv
Momentum = mass x velocity
SI units: kg●m/s
• Vector quantity – direction matches
the velocity
Momentum
Momentum
• If both of these objects are moving down
the street at the same speed… which has
the greater momentum?
• What about if the Mack truck is at rest…
what object has the greatest momentum?
Roll
Tide!!
Practice Problems
• A 2250 kg pick up truck has a velocity of
25 m/s to the east. What is the momentum
of the truck?
p = 5.6x104 kg●m/s
to the east
Practice
• A 21 kg child on a 5.9 kg bike is riding with
a velocity of 4.5 m/s to the northwest.
 What is the total momentum of the child and
the bike together?
 What is the momentum of the child?
 What is the momentum of the bike?
Impulse-Momentum Theorem
• Impulse = product of the force and the
time over which the force acts on an object
Impulse-Momentum Theoren
FΔt= Δp or F Δt= Δp=mvf -mvi
Force x time interval = change in momentum
Practice
• A 1400 kg car moving westward with a
velocity of 15m/s collides with a utility pole
and is brought to rest in 0.30s. Find the
force exerted on the car during the
collision.
F = 7.0 x 104 N to the
east
Stopping Distance
• Stopping times and distance depend on
impulse momentum theorem
• Force is reduced when the time interval of
impact is increased
Stopping
Time
Ft = Ft
Practice
• A 2240 kg car traveling west slows down
uniformly from 20.0m/s to 5.00m/s. How
long does it take the car to decelerate if
the force on the car is 8410 N to the east?
How far does the car travel during the
deceleration?
Impulse-Momentum Theorem