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As a rock of mass 4 kg drops from the edge of a 40-meter-high cliff, it experiences air resistance, whose average strength during the descent is 20 N. at what speed will the rock hit the ground? |
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Answer» 8m/s `K_(i)+U_(i)+W_(r)=K_(f)+U_(f)` `0+mgh-F_(r)h=(1)/(2)mv^(2)+0` `v=sqrt((2h(mg-F_(r)))/(m))` `sqrt((2(40m)[(4kg)(10N//kg)-20N])/(4kg))` `=sqrt((2(40m)[20N])/(4kg))` `=sqrt(2(10)(20)(m^(2))/(s^(2)))` `=20m//s` Again, `W_("total")=DeltaK` COULD also be used. |
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