For a Q in which we are firing a bullet of 0.04kg onto a wooden block which is stopped after a distance of 60cm after penetrating inside it. It’s u=90m/s.
For this Q , we can find a=-6750m/s^2. Using$ v^2 = u^2 +2as$
Now, this a can also be compared with a body moving with$ -6750 m/s^2 $.Not necessarily a wooden block needs to be there.
Then , second point. My book provides average resistive force by the block on bullet = $0.04*6750=270N.$
Now , I am confused since the mass of block is not given . How can find the average resistive force exerted by it.
One way I though of is this but I am not sure if it correct or wrong.
So , using Newton’s third law here.
Force by the bullet on block = -( Force by block on bullet). OR Force by bullet on block = -(force by bullet on block ). Both are not similar here, why is that?
$0.04*(-6750) $= -(mass of wooden block * -6750). So , in the end we force has to be equal. Therefore , we considered F=270N since finding force by bullet on block is not what Q asked. It asked is the average resistive force by block on bullet.
Is writing average here really necessary ?