A bullet of mass 20 g moving with a speed of 75 m/s hits a fixed wooden plank and comes to rest after penetrating a distance of 5 m. what is the average resistive force exerted by the wooden plank on the bullet?

Dear student,
As per the given values it is very easy to find the resistive force with basic concepts.
Force= mass*acc.
Here the bullet travels 5m deep before coming to a halt.
So using the newtons equation we should first find the resistive acc of the bullet.
As we already know the mass of the bullet we can find the force.
V² = U² + 2AS
​Here as the final velocity of bullet is zero then V = 0.
So U² = -2AS
​Now use the given value..
75*75/2*5 = -a
-562.5=a
F=ma
F= 20*10^-3 * (-562.5)
F = 11.25N.
Hope this was more helpful as i explained everything in detail.
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