Question

A bullet of mass 50g moving with a velocity 400ms-1 sticks a wall and goes out from other side with velocity of 100ms-1 . Calculate the work done in passing through the wall

Answer 1

Answer: 3750 J

Explanation:

As work = Force * displacement

Or W = F * s

It can be also written as W = m * a * s

Now, velocity of bullet before hitting the tree is u and is 400 m s-1 and after hitting the tree is v and is 100 m s-1

Apply the 3rd equation of motion , v 2 = u 2 + 2 a s

here , velocity decreases so body retards and equation also changes as v 2 = u 2 - 2 a s

put u = 400 m s-1  and v = 100 m s-1

=> ( 100 )2 = ( 400 )2  - 2 a s

=> 2 a s = ( 400 )2 - ( 100 )2

=> 2 a s = ( 400 - 100 )( 400 + 100 )  

=> 2 a s = 300 * 500

=>  a s = 75000 ............. ( 1 )  

Now W = m * a * s

as m and a * s are given  

put these given values in the above given equation

So W = ( 50 / 1000 ) { as work is measured in J ,so for Joules mass is considered in kgs } * 75000

=> W = 50 * 75

=. W = 3750 J

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