The figure ( http://www.webassign.net/serpse/p5-15.gif )shows a worker poling a

Question

The figure (http://www.webassign.net/serpse/p5-15.gif)shows a worker poling a boat-a very efficient mode oftransportation-across a shallow lake. He pushes parallel to thelength of the light pole, exerting on the bottom of the lake aforce of 225 N. Assume the pole liesin the vertical plane containing the boat's keel. At one moment,the pole makes an angle of 30.0° with thevertical and the water exerts a horizontal drag force of 47.5 N onthe boat, opposite to its forward velocity of magnitude 0.857 m/s.The mass of the boat including its cargo and the worker is375 kg. (a) The water exerts a buoyant force verticallyupward on the boat. Find the magnitude of this force.
1 N

(b) Model the forces as constant over a short interval of time tofind the velocity of the boat 0.200 safter the moment described.
2 m/s
(a) The water exerts a buoyant force verticallyupward on the boat. Find the magnitude of this force.
1 N

(b) Model the forces as constant over a short interval of time tofind the velocity of the boat 0.200 safter the moment described.
2 m/s

Explanation / Answer

(a) buoyant force vertically upward on the boat. isF we have in the viertical direction, net forces=0 225*cos30 +F=m*g=375*9.8 => F=3480.1 N (b)in short interval of time , it canestimate that the force acting on the boat isunchanged, accordingly its acceleration is alsoconstant in horizontal direction: 225*sin30 -47.5=375*a => a=0.173 m/s2 => velocity v=a*0.2+0.857=0.892 m/s => velocity v=a*0.2+0.857=0.892 m/s

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