I have been working these problems and can not seem to get the right answer! A r

Question

I have been working these problems and can not seem to get the right answer!
A rifle with a weight of 20 N fires a 3.0 g bullet with a speed of 240 m/s.
(a) Find the recoil speed of the rifle.
m/s for this part the answer is .352 which is right..


(b) If a 800 N man holds the rifle firmly against his shoulder, find the recoil speed of the man and rifle.
for this part I keep getting .0112 m/s.. which is 10% off of the correct answer

2.Consider a frictionless track as shown in Figure P6.48. A block of mass m1 = 4.05 kg is released from A. It makes a head on elastic collision at B with a block of mass m2 = 11.5 kg that is initially at rest. Calculate the maximum height to which m1 rises after the collision.

I arrived at 1.251... which is close but not correct...

*Can anyone tell me where I am going wrong in my calculations?

Explanation / Answer

1)
Maas of the bullet m = 3 g = 3*10^-3 Kg Mass of rifle M = 20/9.8 = 2.04 Kg Initial speed of the bullet u = 240 m/s (a) (a) From law of conservation of momentum                         0 = mu + Mv Recoil speed of the rifle v = -(m/M)u = -0.352 m/s    (b) Mass of the person M' = 800/9.8 = 81.63 Kg Again from law of conservation of momentum Recoil speed of man & rifle, v = -[m/(M' + M)]u                                                                                             = -[0.003/83.67]*240                                               = - 0.0086 m/s Our rules not allowed us to answer more than one question in one post.Sorry.post seperately the second question.                              Our rules not allowed us to answer more than one question in one post.Sorry.post seperately the second question.

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