PhysicsLAB AP Free Response Question
2007 B1

 
An empty sled of mass 25 kg slides down a muddy hill with a constant speed of 2.4 m/sec. The slope of the hill is inclined at an angle of 15° with the horizontal as shown in the figure above.
 
 (a) Calculate the time it takes the sled to go 21 meters down the slope.

 (b) On the dot below that represents the sled, draw and label a free-body diagram for the sled as it slides down the slope.

 (c) Calculate the frictional force on the sled as it slides down the slope.

 (d) Calculate the coefficient of friction between the sled and the muddy surface of the slope.

(e) The sled reaches the bottom of the slope and continues on the horizontal ground. Assume the same coefficient of friction.
 
 i. In terms of velocity and acceleration, describe the motion of the sled as it travels on the horizontal ground.

 
ii. On the axes below, sketch a graph of speed v versus time t for the sled. Include both the sled’ s travel down the slope and across the horizontal ground. Clearly indicate with the symbol the time at which the sled leaves the slope.
 





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