Answers

2016-03-04T08:27:49+05:30
If one plank slows it one ninth let's assume the speed to be 100. So 100- 100x1/9 give the speed after hitting it. (900-100)/9 =800/9 Now, if the bullet is hit by nine planks the speed will be 100-100/9x9 ie 100 So u need nine planks
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