# Has anyone got any questions on momentum?

I need to test myself :(

Thanks :P

Posted Sat 19th January, 2013 @ 12:13 by :) PurpleJaguar (: - Team GR

i quite like this question:

"A cannon of mass 1600kg fired a cannon ball of mass 5.0kg and recoiled at a velocity of 0.25m/s.

a) calculate:

i)the momentum of the cannon when it recoiled

ii)the velocity of the cannon ball when it left the cannon

b) i) show the kinetic energy of the cannon immediately after it recoiled was 50J (H)

ii) calculate the kinetic energy of the cannon ball when it left the cannon (H) "

These are somwhat complicated, but useful for understanding i thought,

(from: AQA Science -P2 Physics)

Answered Sat 19th January, 2013 @ 12:31 by Pearl Alexus

Do you know what the answers are?

Answered Sun 20th January, 2013 @ 10:37 by :) PurpleJaguar (: - Team GR

well yeah according to MYSELF (havent been able to verify them with my teacher yet)

ai) moment. = mass x velocity

mass= 1600kg

velocity = 0.25 m/s

therefore moment. =1600kg x 0.25m/s

= 400kgm/s

aii)rearrange equation: velocity = moment. divided by mass (of cannon ball)

mass = 5 kg

moment.= 400 kgm/s (conservation of momentum> the same for both)

therefore velocity= 400kgm/s over 5

= 80m/s BUT this (cannon ball) would be in the opposite direction as the cannon itself

bi) Kinetic E. = 1/2 x mass x velocity^2 (for cannon)

mass= 1600kg

velocity = o.25 m/s

therefore, K.E.= 1/2 x 1600kg x (0.25m/s)^2

=50 joules

bii) Kinetic E. for cannon ball:

mass = 5 kg

velocity= 80m/s

so, K.E. = 1/2 x 5 x (80m/s)^2

= 16,000 joules

did you get the same results??

Answered Sun 20th January, 2013 @ 14:14 by Pearl Alexus

I got the same answers as you for section B, but for section A I thought you had to do that conservation of momentum thing when mom before=mom after?
Not sure though

:):(

Answered Sun 20th January, 2013 @ 17:26 by :) PurpleJaguar (: - Team GR