How to calculate average accelaration and force when given mass and velocity?

A bullet of mass 15g travelling with a velocity of 150m/s strikes a tree and penetrates a distance of 250mm into the timber before coming to rest. What was the average acceleration of the buleet and what was the average force causing the accleration?





I really appreciate any help!!!|||u^2+2as = v^2


where u = the initial velocity of the bullet.


a = the acceleration(actually deceleration) of the bullet.


s = the distance that the bullet travels in the timber.


v = the final velocity of the bullet.


i.e.,


150^2+2a*(250/1000)=0^2


22500+0.25*2*a = 0


22500+0.5a = 0


0.5a = -22500


a = -45000


The average acceleration(deceleration) of the bullet was 45000ms^(-2).





So, F = ma


= [(15/1000)*(-45000)]N


= 675N in the opposite direction that the bullet was travelling.


The average force that was causing the acceleration(deceleration) was 675N in the opposite direction that the bullet was travelling.|||use (work done by the force=kinetic energy)


v0^2=2*a*s=2*F/m*s


then


a=v0^2/(2*s)=4.5*10^(4) m/s^2 %26lt;-----------


F=m*a=675 N %26lt;-----------------





ps- all moduli, of course.. but it's simple to understand..


not so simple...!!!!