The question below was asked before, but this seems to ignore that the launching

Question

The question below was asked before, but this seems to ignore that the launching machine should have static friction as well, and that would certainly affect initial velocity. I think we have to take into account static friction as well in the calculation, and I guess assume an impulse time of .001 seconds, unless I am totally off track. Given this information, what would be the static friction, assuming all the other parameters given? A 30 kg launching machine fires a 250 gram projectile horizontally at 100 m/s. This causes the machine to slide 1.122 meters in the opposite direction before coming to a rest. a) What is the machine

Explanation / Answer

a) 30v = 0.25*100 = 25

    v = 25/30 = 0.83 m/s

b) acc = v^2/2s = 0.83^2 / 2*1.22 = 0.30 m/s^2

    t = sqrt(2s/a) = sqrt(2*1.22/0.42) = 2.85 sec

c) P = mv = 30*0.83 = 24.9 kgm/s

d) F = ma = 30*0.3 = 9 N

e) acc as calculated above = 0.30 m/s^2

f) mu = a/g = 0.3/9.8 = 0.031

g) surface contact between the machine and land, and between machine and projectile.

h) g'=g/6 = 9.8/6 = 1.6

     net force = 9 - 0.031*30*1.6 = 7.512 N

     a = 7.512/30 = 0.25 m/s^2

    so, s = v^2/2a = 0.83^2/2*0.25 = 1.37 m

    

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