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When some thing is stopped (or slowed), such as a bullet in a block of wood, a ball in mud a javilin in the ground, it is obviously slowed down to the point of stopping. This is commonly called deceleration (which is nothing more than negative acceleration)

This leads to a force, which is often referred to as Resistance, but governed by the same rules / conditions of Force , F = ma, and acceleration can be determined by one of the 3 equations of motion.

If a 75g bullet travels at 450 m/s and stops 1.1 m into a tree, calculate the resistance of the wood.

u = 450

v = 0

s = 1.1

a = ??

so calculate the deceleration (-ive acceleration) and from this calculate the force that the tree imparted on the bullet of mass, m .... because F = ma

Q5) A plane of mass 35T is landing. If it’s speed changes from 500 km/hr to 20 km/hr over 25 km, find

i) It’s deceleration

ii) The force needed to do this

iii) The net force acting on the plane?

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