Changing momentum 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 Circle the correct answers

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 = change in momentum ( kgm/s ) / N (impulse) time taken (s) To reduce body damage * increase the impact time taken (this reduces the impact force)

Impact force = change in momentum ( kgm/s ) / N (impulse) time taken (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 = change in momentum = 800x20 ( kgm/s ) / N (impulse) time taken

Impact force = change in momentum ( kgm/s ) / N (impulse) time taken (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 = change in momentum = 800x20 ( kgm/s ) / N (impulse) time taken 0.01 (s)

Impact force = change in momentum ( kgm/s ) / N (impulse) time taken (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 = change in momentum = 800x20 ( kgm/s ) / N (impulse) time taken 0.01 (s) =

Impact force = change in momentum ( kgm/s ) / N (impulse) time taken (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 = change in momentum = 800x20 ( kgm/s ) / N (impulse) time taken 0.01 (s) = = 1,600,000 N

Impact force = change in momentum ( kgm/s ) / N (impulse) time taken (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 = change in momentum = 800x20 ( kgm/s ) / N (impulse) time taken 0.01 (s) = = 1,600,000 N = 160,000 Kg force ( 200 g) deadly)

Impact force = change in momentum ( kgm/s ) / N (impulse) time taken (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 = change in momentum = 800x20 ( kgm/s ) / N (impulse) time taken 0.01 (s) = = 1,600,000 N = 160,000 Kg force ( 200 g) deadly) How do seat belts save lives?

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.

a) i) p = mv = 10,000 x 60 = ? ……… kgm/s ii) F = change in momentum = ? = ……… N time 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) p = mv = 10,000 x 60 = 600,000 kgm/s ii) F = change in momentum = 600, = 60,000N time 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) p = mv = 10,000 x 60 = 600,000 kgm/s ii) F = change in momentum = 600, = 60,000N time 10 b i) p = mv = 30,000,000 x 8 = ………………. kgm/s ii) F = change in momentum = time 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) p = mv = 10,000 x 60 = 600,000 kgm/s ii) F = change in momentum = 600, = 60,000N time 10 b i) p = mv = 30,000,000 x 8 = 240,000,000 kgm/s ii) F = change in momentum = 240,000, = 400,000N time 600 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. i) p = mv = 70 x 72 = 5,040 kgm/s ii) F = change in momentum time F= 5g = 5x 70 x10 N = 3500 N time = change in momentum = F

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 = 5,040 kgm/s ii) F = change in momentum time F= 5g = 5x 70 x10 N = 3500 N time = change in momentum = 5,040 kgm/s = 1.44 sec F 3500 N