Question

A bullet with mass of 1.80 gg , flying horizontally with the velocity of 350 m/sm/s , then hits a wood ( wood stays still), it penetrates to a depth of 0.140 mm . (consider that there is a constant retarding force).

-How much time needed to stop the bullet?

-Find the force that the wood applies on the bullet?

Answer 1

Mass of bullet=1.8g=0.0018kg
Initial velocity u=350m/s
Final velocity v=0 (since the bullet finally comes to rest)
Penetrating depth of still stays wood s=0.14mm
s=0.00014m
Time taken to come to rest=t
Acceleration of a bullet is a
According to the first equation of the motion,
v=u+at
0=350+at
at=-350..........eq(1)

According to third equation of motion,



Solving for equation 1

Hence,in 0.0008 seconds bullet will penetrate to dept 0.14mm

From Newton's Second law of moton
Force,



Hence, the magnitude of the force exerted by the wood by bullet is 787.5N