Question

A bullet has a mass of 20 grams and is travelling at a velocity of 275 m/s . It passes completely through a wooden block kept horizontally on the table and emerges out with a velocity of 130 m/s. If the block is 1.2 kg in mass, the velocity of the block after the bullet passes through it will be

Answer 1

Answer:

Mass of the bullet =0.2kg=m

1

Mass of the block =10kg=m

2

Initial velocity of bullet=500m/s=v

1

Initial velocity of block=0m/s=v

2

Final velocity of bullet=v

1

′

=100m/s

Final velocity of block=v

2

′

From the conservation of momentum:

m

1

v

1

+m

2

v

2

=m

1

v

1

′

+m

2

v

2

′

0.02×500+10×0=0.02×100+10v

2

′

10=2+10v

2

′

v

2

′

=0.8m/s

After moving a distance of 0.2 the block stops.Therefore change in kinetic energy =work done by friction

0−

2

1

×10×(0.8)

2

=−μ×10×10×0.2

μ=0.16