Q5 of 46 Page 247

A bullet of mass 20 g moving with a speed of 75 ms-1 hits a fixed wooden plank and comes to rest after penetrating a distance of 5 cm. What is the average resistive force exerted by the wooden plank on the bullet?

According to the equations of motion,

v2 – u2 = 2as …eq(1)


where v is the final velocity


u is the initial velocity


a is the acceleration


s is the displacement


From eq (1)


Here u = 75 m/s


v = 0 m/s


s = 5 cm = 0.05 m


So


= -56250 ms-2


Hence average resistive force = ma = 20 g × -56250 ms-2


= 0.02 kg × -56250 ms-2


= -1125 N


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