aww..another physics problem…CONSERVATION OF MOMENTUM?
1.) A hunter a rifle that can fire 60-g bullets with a speed of 900m/s. A 40-kg leopard springs at him at 10 m/s. How many bullets must the hunter fire into the leopard in order to stop him in his tracks
2.) A hunter in a rowboat loses the oars and decides to set the boat in the motion by firing his rifle astern five times. The toal weight of the boat and its contents is 300 lb, the weight of each bullet is 0.40-lb, and the speed of the bullets is 2000 ft/s. Assume the air resistance is negligible. How far does the boat go in 10 minutes.
Please please help me I’m going crazy with these problems…^^
1. solution… since momentum is conserved…
assuming elastic collision…then
mv = n*m’v’
mv – momentum of leopard
m’v’ – momentum of 1 bullet
n – number of bullets
given that
m = 40,000 g
v = 10 m/s
of mv = 400,000 g*m/s
m’ = 60 g
v’ = 900 m/s
or m’v’ = 54,000 g*m/s
thus
54,000*n = 400,000
n = 7.4 bullets
but since there are no 0.4 bullets.. therefore the hunter needs at least 8 bullets to stop the leopard.
2. solution…
mv = n*m’v’
mv – momentum of boat
m’v’ – momentum of 1 bullet
n – bullets
given that
m = 300 lb
v = ?
mv = 300v lb*ft/s
m’ = 0.4 lb
v’ = 2,000 ft/s
n = 5
300v = 5*0.4*2000
300v = 4000
v = 13.33 ft/s
now, v = distance / time
or
distance = v*t
t = 10 minutes or 600 secs
distance = 13.33 ft/s * 600 s = 8000 ft
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