Physics 12 energy, work question

[gdhillon]

Q:A sandbag stops a 12 g bullet which was traveling at 860 m/s. The bullet penetrated a
distance of 24 cm into the sand?
a) How long did it take the bullet to stop?
b) What average force acted on the bullet?
first i used ∇p=Ft so 10.32=18490t t=5.6*10^-4 sec
then i put that into e=1/2mv^2 (to get letter A) so 1/2(.012)860^2= 4437.6

 

[NascentOxygen]

first i used ∇p=Ft so 10.32=18490t

Where did the 18490 come from? The data tells you neither F nor t, only distance.

 

[dreamLord]

You know the distance traveled by the bullet, it's initial velocity, and it's final velocity. Use a kinematics equation which relates them to find out the acceleration of the bullet. Now use that to find the time it travels for using another kinematics equation. And then use that to calculate the average force using the formula you wrote.