A) 4
B) 8
C) 6
D) 10
Correct Answer: B
Solution :
Let the thickness of each plank is s. If the initial speed of bullet is 100 m/s then it stops by covering a distance 2s By applying \[{{v}^{2}}={{u}^{2}}-2as\]Þ \[0={{u}^{2}}-2as\] \[s=\frac{{{u}^{2}}}{2a}\] \[s\propto {{u}^{2}}\] [If retardation is constant] If the speed of the bullet is double then bullet will cover four times distance before coming to rest i.e. \[{{s}_{2}}=4({{s}_{1}})=4(2s)\] Þ \[{{s}_{2}}=8s\] So number of planks required = 8You need to login to perform this action.
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