I know you are supposed to do multiple questions per post, but this was a proble
ID: 2060945 • Letter: I
Question
I know you are supposed to do multiple questions per post, but this was a problem giving to me as homework and I am still trying to figure out how this is done.A toy gun is held horizontally uses a spring to project a 6.5g soft rubber sphere horizontally. The spring constant is 11.0 N/m, the barrel of the gun is 13 cm long, and a constant fictional force of 0.032 N exists between barrel and projectile. (Assume the projectile is in constant contact with the barrel for the full 13.0 cm.) The spring is compressed 5.9 cm for this launch.
A. Find the coefficient of friction. Is it static or kinetic friction?
I know that it is kinetic friction and fk= mk*N but I don't know how to get the coefficient
B. Individually, find the work done by gravity, the spring and friction.
Completely clueless on this one.
C. Find the total work done.
I know that Wtotal = Wc+Wnc = change in KE
D. With what speed does the projectile leave the barrel?
I though you would use V^2= Vo^2 = 2a (x-xo) but I was wrong.
Please help.
Explanation / Answer
a) k=Ff/Fn
Ff=0.032N
Fn=.0065kg*9.8m/s2=.064N
k=.032N/.064N=.5
B) remember that it's the force parallel to the displacement that matters, or W=Fcosd
--for gravity, the displacement is perpendicular, so cos(90)=0. Gravity doesn't do work.
--for the spring, use hook's law to find the force: F=-kx=11.0N/m*(.13m-.059m)=.781N
from 5.9cm the rubber travels 7.1cm, and the force of the spring is parallel to displacement, so.781N*.071m=+.055J (the force is to the right).
--friction is an opposing force, so the work it does will be negative: W=0.032N*.071m=-.002J
C) The total work will just be work from spring minus work from friction: .055J-.002J=.053J
D) The easiest way to do this is to realize all of the energy you just found will be converted into kinetic energy. Wt=1/2mv2.
Solve for v. v=(2*.053J/.0065kg)=4.04m/s
hope that helps