A bullet of mass 20 g is fired from a riffle with a velocity of 800 m $s^{- 1}$ . After passing through a mud wall 100 cm thick, velocity drops to 100 m $s^{- 1}$ . What is the average resistance of the wall? (Neglect friction).

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Solution

Let average resistance= $F$ .
Change in K.E=workdone.
$\frac{1}{2} m v^{2} - \frac{1}{2} m u^{2} = F \times d \frac{1}{2} m (800^{2} - 100^{2}) = F (- 100 \times 10^{- 2})$ negative sign due to displacement is opposite to applied force.
$F = \frac{630000 \times 20 \times 10^{- 2}}{2 \times 0.1} = 6300$ N

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A bullet of mass 20 g is fired from a riffle with a velocity of 800 ms−1 . After passing through a mud wall 100 cm thick, velocity drops to 100 ms−1 . What is the average resistance of the wall? (Neglect friction).

Let average resistance=F.Change in K.E=workdone.12mv2−12mu2=F×d12m(8002−1002)=F(−100×10−2)negative sign due to displacement is opposite to applied force.F=630000×20×10−22×0.1=6300N

A bullet of mass 20 g is fired from a riffle with a velocity of 800 m $s^{- 1}$ . After passing through a mud wall 100 cm thick, velocity drops to 100 m $s^{- 1}$ . What is the average resistance of the wall? (Neglect friction).