Question

A $10$ g bullet moving at $200$ m/s stops after penetrating $5$ cm of wooden plank. The average force exerted on the bullet will be?

• A. $2000$N
• B. $-2000$N
• C. $5000$N
• D. $-4000$N

Answer 1

Answer: (D)

$-4000$N

mass$=10g=10/1000=0.01kg$

Initial speed$=u=200m/s$

final velocity$=om/s$

$S=5cm=5/100=0.05m$

From third equation of motion :$V²-u²=2as$

$0²-\left(200\right)²=2ax0.05$

$-40000=ax5x2/100$

$-40000=a/10$

$a=-400000m/s²$

From Newton's Second law:

$F=ma$

$=0.01x(-400000)$

$=-4000N$

A force of $4000N$ acts in the opposite direction.