PhysicsLAB AP Free Response Question
2011 B4

A beaker weighing 2.0 N is filled with 5.0 x 10-3 m3 of water. A rubber ball weighing 3.0 N is held entirely underwater by a massless string attached to the bottom of the beaker, as represented in the figure below. The tension in the string is 4.0 N. The water fills the beaker to a depth of 0.20 m. Water has a density of 1000 kg/m3. The effects of atmospheric pressure may be neglected.
 
 
 (a) Calculate the weight of the entire apparatus.

 
(b) On the dot below that represents the ball, draw and label the forces (not components) that act on the ball.
 
 

 (c) Calculate the buoyant force exerted on the ball by the water. If you need to draw anything other than what you have shown in part (b) to assist in your solution, use the space below. Do NOT add anything to the figure in part (b).

 (d) Calculate the pressure due to the liquid (the gauge pressure) at the bottom of the beaker.

 
(e) The string is cut, and the ball rises to the surface and floats. Indicate whether the water level is higher, lower, or the same after equilibrium is reached. Justify your answer.
 
____ Higher
____ Lower
____ The same
 





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