Question

A bullet having a mass of 10g and moving with speed of 1.5 m/s penetrates a thick wooden plank of mass 900g the plank was initial celocity at rest determine their velocity

Answer 1

This is the question of momentum conservation.

Treat bullet and wooden plank as a part of the system. Hence, the forces between them will be internal forces, which cannot change the momentum of the system.

Hence, initial momentum = Final momentum

Initial momentum = 0.01 × 1.5 = 0.015 kg m/s

Let the common velocity after the penetration be v.

Final momentum = (0.9 + 0.01)×v

Now,

0.91 × v = 0.015

v = 0.0165 m/s

Hence, the velocity after penetration = 0.0165 m/s

Answer 2

Given: Mass of bullet (m¹)= 10g= 0.010kg.

Mass of plank (m²)= 90g= 0.090kg.

Initial velocity of bullet (u¹)= 1.5m/s.

Initial velocity of plank (u²)= 0m/s.

To find: Common velocity (v)= ?

Formula: m¹u¹+ m²u²= m¹v¹+ m²v²

Solñ: Let v¹and v² be the common velocities of the bullet and plank.

v¹= v²= v

m¹u¹+ m²u²= m¹v¹+ m²v²

(0.01×1.5)+ (0.09×0)= (0.01×v)+ (0.09×v)

0.015+0= v (0.01+0.09)

0.015= 0.1v

v= 0.015/ 0.1

v= 0.15 m/s

Ans: The plank moves with a velocity of 0.15 m/s.