3.

A 2,000-kilogram car uses a braking force of 12,000 newtons to stop in 5 seconds.

a. What impulse acts on the car?

b. What is the change in momentum of the car?

c. What is the initial speed of the car?

m = 2,000-kilogram

F = 12,000

t = 5 seconds

a) Impulse (I) = Ft = 12000 * 5

I = 60,000 Ns

b) from Newton's 2nd law

F = m∆v/t

Ft = m∆v

change in momentum (∆p) = 60,000kgm/s

c) ∆v = Ft/m = 60,000/2000 = 30m/s

the initial velocity is 30m/s since final velocity is zero

Momentum ...

is a quantity that describes an object's

resistance to stopping (a kind of "moving

inertia"). and is represented by the symbol p which is the product of an object's mass and velocity.

p = m v

is a vector quantity (since velocity is a

vector and mass is a scalar).

Impulse ...

is a quantity that describes the effect of a

net force acting on an object (a kind of

"moving force").

is represented by the symbol I

is the product of the average net force

acting on an object and its duration.

I = F Δ t