A police officer fires a bullet of mass 50.0 g with speed 200 ms-1 on soft plywood of some thickness. The bullet emerges with speed 100 ms-1 from other side. Using work energy theorem, find the work done by plywood in reducing the speed of bullet?
(a) – 50 J (b) – 550 J (c) – 750 J (d) – 200 J
Answers
Answer:
(a) – 50 J
Explanation:
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Given : A police officer fires a bullet of mass 50.0 g with speed 200 m/s
on soft plywood of some thickness.
The bullet emerges with speed 100 m/s from other side.
To Find : work energy theorem, find the work done by plywood in reducing the speed of bullet?
(a) – 50 J (b) – 550 J (c) – 750 J (d) – 200 J
Solution:
the total work done on a particle is equal to the change in the kinetic energy of that particle
Kinetic energy = (1/2) * mass * ( velocity )²
m = 50 g = 50/1000 kg = 1/20 kg
Initial KE = (1/2) * (1/20) * 200²
= 1000 Joule
Final KE = (1/2) * (1/20) * 100²
= 250 Joule
total work done = 250 - 1000 = - 750 Joule
the work done by plywood in reducing the speed of bullet = – 750 J
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