Question

a object of mass 4 kg is dropped from a height 20m. it reaches the ground with a speed of 16m/sec .Work done on the body by air friction

Answer 1

卄乇ㄚ 千尺丨乇几ⅅ

卄乇尺乇 丨丂 ㄚㄖ凵尺

卂几丂山乇尺


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⊙ Mass = 4kg

⊙ h (s) = 20m

⊙ U = 0 m/sec

⊙ V = 16m /sec


Using the 3rd equation of motion......


$v {}^{2} = u {}^{2} + 2as \\ \\ 256 = 40a$



$a = \frac{256}{40} = 6.4$


so, a = 6.4 m/s^2.


Now ,
$f = ma \\ \\ f = 4 \times 6.4 = 25.6n$




Now ,


$w = fs \\ \\ w = 25.6 \times 20 = 512joules$



so, workdone is 512 joules.



Hope it helps you



$<marquee > prabhudutt$

Answer 2

heya !!


please refer this attachment


Thanks!!