Transcript No Slide Title

Changing momentum
Circle the correct answers
What does a force do to the momentum of an object
by a front-end impact? increase /decrease momentum
by a rear-end impact
increase /decrease momentum
In an accident large
forces act on the car.
It is important that
these do not crush
the part of the car
where people sit
Modern cars have a welded cage to protect passengers.
In an accident large
forces act on the car.
It is important that
these do not crush
the part of the car
where people sit
Modern cars have a welded cage to protect passengers.
The rest of the car is
designed to bend
and distort.
This will let the impact
take longer
The car comes to a stop more slowly so the forces are not so big.
Impact force
/ N (impulse)
=
change in momentum
time taken
( kgm/s )
(s)
To reduce body damage
* increase the impact time taken
(this reduces the impact force)
Impact force
/ N (impulse)
=
change in momentum
time taken
( kgm/s )
(s)
Example problem:
An 800Kg car crashes into a wall and is brought to rest in 0.01 seconds from
a velocity of 20m/s ( about 50mph ).
Calculate the impact force.
Impact force
/ N (impulse)
=
change in momentum =
time taken
800x20
( kgm/s )
Impact force
/ N (impulse)
=
change in momentum
time taken
( kgm/s )
(s)
Example problem:
An 800Kg car crashes into a wall and is brought to rest in 0.01 seconds from
a velocity of 20m/s ( about 50mph ).
Calculate the impact force.
Impact force
/ N (impulse)
=
change in momentum =
time taken
800x20
0.01
( kgm/s )
(s)
Impact force
/ N (impulse)
=
change in momentum
time taken
( kgm/s )
(s)
Example problem:
An 800Kg car crashes into a wall and is brought to rest in 0.01 seconds from
a velocity of 20m/s ( about 50mph ).
Calculate the impact force.
Impact force
/ N (impulse)
=
change in momentum =
time taken
800x20
0.01
=
16000
0.01
( kgm/s )
(s)
Impact force
/ N (impulse)
=
change in momentum
time taken
( kgm/s )
(s)
Example problem:
An 800Kg car crashes into a wall and is brought to rest in 0.01 seconds from
a velocity of 20m/s ( about 50mph ).
Calculate the impact force.
Impact force
/ N (impulse)
=
change in momentum =
time taken
=
=
800x20
0.01
( kgm/s )
(s)
16000
0.01
1,600,000 N
Impact force
/ N (impulse)
=
change in momentum
time taken
( kgm/s )
(s)
Example problem:
An 800Kg car crashes into a wall and is brought to rest in 0.01 seconds from
a velocity of 20m/s ( about 50mph ).
Calculate the impact force.
Impact force
/ N (impulse)
=
change in momentum =
time taken
=
=
=
160,000
800x20
0.01
( kgm/s )
(s)
16000
0.01
1,600,000 N
Kg force ( 200 g) deadly)
Impact force
/ N (impulse)
=
change in momentum
time taken
( kgm/s )
(s)
Example problem:
An 800Kg car crashes into a wall and is brought to rest in 0.01 seconds from
a velocity of 20m/s ( about 50mph ).
Calculate the impact force.
Impact force
/ N (impulse)
=
change in momentum =
time taken
=
How do seat belts
save lives?
=
=
160,000
800x20
0.01
( kgm/s )
(s)
16000
0.01
1,600,000 N
Kg force ( 200 g) deadly)
Now try these questions:
Q1. Calculate the initial momentum and the impact force
in the following situations.
a)
A 10,000 kg plane is brought to rest on a runway
from a velocity of 60m/s (about 150 mph) in 10 seconds
b)
A 30,000 ton container ship boat is brought to rest
from a velocity of 8 m/s (about 20 mph) in 600 seconds
1 ton = 1000kg approx
Q2
If the maximum force allowed
on a pilot using a catapult to
take off from an aircraft carrier
is 5g ,
if his mass is 70kg and the
take off velocity must reach 72m/s ,
calculate the time spent on
the catapult.
Now try these questions:
Q1. Calculate the initial momentum and the impact force
in the following situations.
a)
A 10,000 kg plane is brought to rest on a runway
from a velocity of 60m/s (about 150 mph) in 10 seconds
b)
A 30,000 ton container ship boat is brought to rest
from a velocity of 8 m/s (about 20 mph) in 600 seconds
1 ton = 1000kg approx
a) i)
ii)
p = mv
= 10,000 x 60 =
F = change in momentum =
time
?
……… kgm/s
? = ……… N
10
Now try these questions:
Q1. Calculate the initial momentum and the impact force
in the following situations.
a)
A 10,000 kg plane is brought to rest on a runway
from a velocity of 60m/s (about 150 mph) in 10 seconds
b)
A 30,000 ton container ship boat is brought to rest
from a velocity of 8 m/s (about 20 mph) in 600 seconds
1 ton = 1000kg approx
a) i)
ii)
p = mv
= 10,000 x 60 = 600,000 kgm/s
F = change in momentum = 600,000 - 0
time
10
= 60,000N
Now try these questions:
Q1. Calculate the initial momentum and the impact force
in the following situations.
a)
A 10,000 kg plane is brought to rest on a runway
from a velocity of 60m/s (about 150 mph) in 10 seconds
b)
A 30,000 ton container ship boat is brought to rest
from a velocity of 8 m/s (about 20 mph) in 600 seconds
1 ton = 1000kg approx
a) i)
ii)
b
i)
ii)
p = mv
= 10,000 x 60 = 600,000 kgm/s
F = change in momentum = 600,000 - 0
time
10
p = mv
= 30,000,000 x 8 =
F = change in momentum =
time
……………….
= 60,000N
kgm/s
Now try these questions:
Q1. Calculate the initial momentum and the impact force
in the following situations.
a)
A 10,000 kg plane is brought to rest on a runway
from a velocity of 60m/s (about 150 mph) in 10 seconds
b)
A 30,000 ton container ship boat is brought to rest
from a velocity of 8 m/s (about 20 mph) in 600 seconds
1 ton = 1000kg approx
a) i)
ii)
b
i)
ii)
p = mv
= 10,000 x 60 = 600,000 kgm/s
F = change in momentum = 600,000 - 0
time
10
p = mv
= 30,000,000 x 8 =
F = change in momentum =
time
= 60,000N
240,000,000 kgm/s
240,000,000 - 0
= 400,000N
600
Q2
If the maximum force allowed
on a pilot using a catapult to
take off from an aircraft carrier
is 5g ,
if his mass is 70kg and the
take off velocity must reach 72m/s ,
calculate the time spent on
the catapult.
i)
p = mv
= 70 x 72
ii)
F = change in momentum
time
=
F= 5g = 5x 70 x10 N = 3500 N
time =
change in momentum =
F
5,040 kgm/s
Q2
If the maximum force allowed
on a pilot using a catapult to
take off from an aircraft carrier
is 5g ,
if his mass is 70kg and the
take off velocity must reach 72m/s ,
calculate the time spent on
the catapult.
i)
p = mv
= 70 x 72
ii)
F = change in momentum
time
=
5,040 kgm/s
F= 5g = 5x 70 x10 N = 3500 N
time =
change in momentum =
F
5,040 kgm/s
3500 N
=
1.44 sec