The Student Room Group

M1 Help again .... Conseravtion of Momentum

Could someone explain to me how to do:


A gun of mass 5000kg discharges a shot of mass 25kg. The gun recoils against a constant force of 10kN which brings it to rest in 1.25/s . Find the speet of the shot.

ALl impulses questions are pretty easy. This one probably is as well but i have forgotten how to include and use the resistance force!!!

Please help ASAP.


ALso

Where can i find M1 papers with Markschemes?

Thanks all , your so helpful! :wink:
Reply 1
A mass of 5000 kg comes to rest in 1.25 sec under a force of 10 Kn. Find its initial velocity?

Can you do that one ?
Reply 2
before force is applied:
before releasing the shot: both are at reast
after releasing the shot: shot has velocity v, gun has velocity -u ( because in the opposite direction)
25xv + 5000x-u = 0
200u = v

now force is applied:
Impulse = change in momentum
10000x1.25 = 5000(u)
u = 2.5 ms-1

v = 200x2.5 = 500 ms-1
Reply 3
MAC1205
Could someone explain to me how to do:


A gun of mass 5000kg discharges a shot of mass 25kg. The gun recoils against a constant force of 10kN which brings it to rest in 1.25/s . Find the speet of the shot.

ALl impulses questions are pretty easy. This one probably is as well but i have forgotten how to include and use the resistance force!!!

Please help ASAP.


ALso

Where can i find M1 papers with Markschemes?

Thanks all , your so helpful! :wink:


The impulse the gun receives (what it recoils with) is
P = Ft = 10x103 x 1.25
P = 1.25x104

The shell must have this momentum too, so:
P = mv => v = P/m
v = 1.25x104/25 = 500

edit: someone beat me to it!
Reply 4
Thanks Everyone ! :biggrin: :biggrin:
Reply 5
can someone explain to me showing me the full steps using m1u1+m2u2=m1v1+m2v2 as i cant picture whats going on
Reply 6
m1 = mass of gun
m2 = mass of bullet
u1 = initial speed of gun
u2 = initial speed of bullet
v1 = speed of gun
v2 = speed of bullet

m1u1 + m2u2 = m1v1 + m2v2
0 + 0 = 5000(-v1) + 25(v2), since they're initially at rest.
25v2 = 5000v1
v2 = 200v1 (1)

Impulse = m1v1 - m1u1 = 5000v1 - 0
Impulse = Ft = 10000*1.25 = 12500 Ns

Equating those two:
12500 = 5000v1
v1 = 2.5 m/s

Plugging this in (1):
v2 = 200v1 = 200*2.5 = 500 m/s