This preview shows pages 1–6. Sign up to view the full content.
Impulse of a force
Impulse
(
I
)
of a force is the product of the
force and duration of action of the force.
If a force
F N
acts on an object for a time
∆
t
,
then
I = F
∆
t
But force is a measure of the rate of change
of the rate of change of momentum.
P
Impulse of a force is a measure of the change
in momentum it produces on an object.
P
F
t
∆
=
∆
∆
I = F
∆
t =
×
∆
t =
∆
t
∆
P
Impulse is measured in
Ns
which is the same a
kgms
1
.
When you drive a nail down, the longer
the hammer stays in contact with the
nail, the smoother will be the drive.
1
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document When a 0.2 kg baseball is hit, its velocity changes from 25
ms
1
to 25 ms
1
. (a) What is the impulse delivered by the
bat to the ball? (b) If the ball is in contact with the bat for
1.1 ms, what is average force on the ball?
m = 0.2 kg, v
i
= 25 ms
1
, v
f
= 25 ms
1
,
∆
t = 1.1 ms = 1.1 × 10
3
s
P
i
= mv
i
= 0.2 kg × 25 ms
1
= 5 kgms
1
.
P
f
= mv
f
= 0.2 kg × (25 ms
1
) = 5 kgms
1
.
= P
kgms
1
kgms
1
0 kgms
1
ave
∆
P
(b)
F =
∆
t
∆
P = P
f
– P
i
= 5 kgms
– 5 kgms
= 10 kgms
.
(a)
I =
∆
P = 10 kgms
1
.
1
3
10 kgms
=
1.1
10 s
×
v
i
= 25 ms
1
v
f
= 25 ms
1
3
9.1×10 N = 9.1 kN
=
2
Elastic and inelastic collisions
Momentum
P
is conserved in all types of collisions
Kinetic energy
K
may or may not be
conserved in a particular collision.
If no energy is lost in deforming the
objects then
K
will be conserved.
A collision where momentum and energy both
are conserved is called an
elastic collision
.
For an elastic collision,
P
i
= P
f
and K
i
= K
f
.
For an inelastic collision
,
P
i
= P
f
but K
f
< K
i
If K
f
is not the same as K
i
, the
collision is said to be
inelastic.
3
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document Let us consider an object of mass
m
1
moving to the right with a velocity
v
1i
A second object of mass
m
2
moves to
e left with a velocity
i
m
1
v
1i
m
2
v
2i
v
1f
v
2f
the left with a velocity
v
2i
.
They collide and object 1 moves away with a velocity
v
1f
The velocity of object 2 after collision is
v
2f
The momentum of object 1 before collision P
1i
= m
1
v
1i
The momentum of object 2 before collision P
2i
= m
2
v
2i
Total momentum before collision
P
i
= m
1
v
1i
+ m
2
v
2i
Total momentum after collision
P
f
= m
1
v
1f
+ m
2
v
2f
4
Since momentum is conserved,
P
i
= P
f
m
1
v
1i
+ m
2
v
2i
= m
1
v
1f
+ m
2
v
2f
m
1
(v
1i
– v
1f
) = m
2
(v
2f
– v
2i
)
….(i)
The initial kinetic energy of the two objects
2
2
i
1 1i
2
2i
1
1
K =
m v
+
m v
2
2
The total kinetic energy after collision
For an elastic collision, the
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 05/01/2011 for the course PHY 2048 taught by Professor George during the Fall '10 term at Edison State College.
 Fall '10
 George
 Physics, Force, Momentum

Click to edit the document details