Given, mass of bullet, mb=30g=0.03‌kg Velocity of bullet, vb=700ms−1 Mass of block, mB=4‌kg Height upto which block rises, h=0.2m Before collision, momentum of bullet =mb×vb =0.03×700 =21‌kg−ms−1 Let v1,v2 be the velocities of bullet and block after the collision. Using conservation of momentum, ⇒ 21=0.03×v1+4v2 ...(i) Using conservation of energy for the block, Change in KE = Work done
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mBv22=mBgh ⇒ v22=2gh ⇒ v2=√2×9.8×0.2 =1.979ms−1 Putting the value of v2 in Eq. (i), we get 21=0.03×v1+4×1.979 ⇒ 21=0.03×v1+7.919 ⇒ 21−7.919=0.03×v1 ⇒ v1=