Question

The work done to bring a body moving with a velocity of 6 m/s to rest is 72 J. What is the mass of the body ? 
​

Answer 1

Given : m

1

=2kg m

2

=1kg u

1

=3 m/s u

2

=4 m/s

Let the common velocity of the combined body be V

Mass of combined body M=2+1=3kg

Applying conservation of momentum :

2×3−1×4=3×V ⟹V=

3

2

m/s

Momentum of the system P=2×3−1×4=2 kg m/s

Loss in kinetic energy of the system due to collision ΔK.E=K.E

i

−K.E

f

ΔK.E=

2

1

(2)×3

2

+

2

1

(1)×4

2

−

2

1

(3)×(

3

2

)

2

⟹ΔK.E=

3

49

J