Physics..help please
posted by jake on .
A rifle with a weight of 35 N fires a 4.0 g bullet with a speed of 250 m/s.
(a) Find the recoil speed of the rifle.
___m/s
(b) If a 700 N man holds the rifle firmly against his shoulder, find the recoil speed of the man and rifle.
___m/s

Ah, do this the same way we did the guy on skates.

I need help with the same question but different numbers. how do you solve it?

Go look at the last problem I did with jake, wait a sec and I will copy it here, conservation of momentum with zero before the shot.

A 715 N man stands in the middle of a frozen pond of radius 10.0 m. He is unable to get to the other side because of a lack of friction between his shoes and the ice. To overcome this difficulty, he throws his 1.2 kg physics textbook horizontally toward the north shore at a speed of 10.0 m/s. How long does it take him to reach the south shore?
* Physics..help please  Damon, Wednesday, October 6, 2010 at 3:51pm
first find his mass in kilograms
m = 715 / 9.81
then use conservation of momentum
(total of 0 before the toss)
0 = (715/9.81) v  1.2 * 10
solve for v
how long does it take to go 10 meters at v meters/second? 
I still can't figure it out with this question. i get the one you did with jake but not this one.

A rifle with a weight of 35 N fires a 4.0 g bullet with a speed of 250 m/s.
(a) Find the recoil speed of the rifle.
___m/s

All is still. Momentum = 0
A shot rings out.
The rifle goes left, the bullet goes right.
Momentum is STILL zero (no outside forces)
m rifle = 35/9.8
m bullet = .004
so
0 = (35/9.8) v + .004 * 250 
for the second part add the mass of the man (700/9.8) to the mass of the rifle and repeat the calculation

A bullet is shot from a rifle aimed horizontally at the same time a bullet is dropped from the same height as the gun's barrel. Which bullet hits the ground first?