Answer:
The speed of the plank is 81.68 m/s
Step-by-step explanation:
Given that,
Speed of bullet = 152 m/s
Speed of wood = 128 m/s
Speed of another bullet = 97 m/s
We need to calculate the speed of plank
Using conservation of momentum

Where,
u = initial velocity
v = final velocity
....(I)
....(II)
From equation(I) and equation(II)



Hence, The speed of the plank is 81.68 m/s