如图所示，水池池壁是一个斜面，池中装有深度为h的水，池底a点到水面b点之间的距离为l．现要将一质量为m的铁块从a匀速拖到b，此过程中斜面的机械效率为η．水和铁块的密度分别是ρ水

Question

如图所示，水池池壁是一个斜面，池中装有深度为h的水，池底a点到水面b点之间的距离为l．现要将一质量为m的铁块从a匀速拖到b，此过程中斜面的机械效率为η．水和铁块的密度分别是ρ_水和ρ_铁．
求：（1）铁块在池底所受的水对它的压强p；
（2）将铁块从a拖到b所做的有用功W_有；
（3）拖动过程中铁块所受的阻力f．
<sub>水铁

有</sub>

Answer 1

（1）铁块在池底受到水对它的压强P=ρ_水水gh．
答：铁块受到的压强为ρ_水水gh．
（2）W_有用有用=（G-F_浮浮）h
=（mg-ρ_水水gV_排排）h
=（mg-ρ水g(m)/(ρ铁)）h
=(mgh(ρ铁−ρ水))/(ρ铁)．
答：有用功为(mgh(ρ铁−ρ水))/(ρ铁)．
（3）W总＝(W有用)/(η)＝ (mgh(ρ铁−ρ水))/(ηρ铁)，
W_额=W_总-W_有用
=(mgh(ρ铁−ρ水))/(ηρ铁)−(mgh(ρ铁−ρ水))/(ρ铁)=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． ρ水g(m)/(ρ铁)）h
=(mgh(ρ铁−ρ水))/(ρ铁)．
答：有用功为(mgh(ρ铁−ρ水))/(ρ铁)．
（3）W总＝(W有用)/(η)＝ (mgh(ρ铁−ρ水))/(ηρ铁)，
W_额=W_总-W_有用
=(mgh(ρ铁−ρ水))/(ηρ铁)−(mgh(ρ铁−ρ水))/(ρ铁)=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． 水g(m)/(ρ铁)mmmρ铁ρ铁ρ铁铁）h
=(mgh(ρ铁−ρ水))/(ρ铁)．
答：有用功为(mgh(ρ铁−ρ水))/(ρ铁)．
（3）W总＝(W有用)/(η)＝ (mgh(ρ铁−ρ水))/(ηρ铁)，
W_额=W_总-W_有用
=(mgh(ρ铁−ρ水))/(ηρ铁)−(mgh(ρ铁−ρ水))/(ρ铁)=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． (mgh(ρ铁−ρ水))/(ρ铁)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)铁−ρ水)水)ρ铁ρ铁ρ铁铁．
答：有用功为(mgh(ρ铁−ρ水))/(ρ铁)．
（3）W总＝(W有用)/(η)＝ (mgh(ρ铁−ρ水))/(ηρ铁)，
W_额=W_总-W_有用
=(mgh(ρ铁−ρ水))/(ηρ铁)−(mgh(ρ铁−ρ水))/(ρ铁)=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． (mgh(ρ铁−ρ水))/(ρ铁)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)铁−ρ水)水)ρ铁ρ铁ρ铁铁．
（3）W总＝(W有用)/(η)＝ (mgh(ρ铁−ρ水))/(ηρ铁)，
W_额=W_总-W_有用
=(mgh(ρ铁−ρ水))/(ηρ铁)−(mgh(ρ铁−ρ水))/(ρ铁)=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． W总＝(W有用)/(η)＝ (mgh(ρ铁−ρ水))/(ηρ铁)，
W_额=W_总-W_有用
=(mgh(ρ铁−ρ水))/(ηρ铁)−(mgh(ρ铁−ρ水))/(ρ铁)=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． 总＝(W有用)/(η)W有用W有用W有用有用ηηη＝ (mgh(ρ铁−ρ水))/(ηρ铁)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)铁−ρ水)水)ηρ铁ηρ铁ηρ铁铁，
W_额额=W_总总-W_有用有用
=(mgh(ρ铁−ρ水))/(ηρ铁)−(mgh(ρ铁−ρ水))/(ρ铁)=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． (mgh(ρ铁−ρ水))/(ηρ铁)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)铁−ρ水)水)ηρ铁ηρ铁ηρ铁铁−(mgh(ρ铁−ρ水))/(ρ铁)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)mgh(ρ铁−ρ水)铁−ρ水)水)ρ铁ρ铁ρ铁铁=fl
所以阻力f=((1−η)mgh(ρ铁−ρ水))/(lηρ铁)．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． ((1−η)mgh(ρ铁−ρ水))/(lηρ铁)(1−η)mgh(ρ铁−ρ水)(1−η)mgh(ρ铁−ρ水)(1−η)mgh(ρ铁−ρ水)铁−ρ水)水)lηρ铁lηρ铁lηρ铁铁．
答：阻力为((1−η)mgh(ρ铁−ρ水))/(lηρ铁)． ((1−η)mgh(ρ铁−ρ水))/(lηρ铁)(1−η)mgh(ρ铁−ρ水)(1−η)mgh(ρ铁−ρ水)(1−η)mgh(ρ铁−ρ水)铁−ρ水)水)lηρ铁lηρ铁lηρ铁铁．