# Q3S - being accelerated to the right as shown The...

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Quiz 3 Solutions Check the best answer. 1. Which of these statements about work and energy is wrong? The work done by a constant force is independent of the path followed. The potential energy change for a conservative force is the negative of the work it does. A static friction force exerted by a stationary surface does no work. If all external forces are conservative, total mechanical energy is conserved. [Internal and external.] Check T or F depending on whether the statement is true or false. 2. A ball is thrown straight up into the air. Taking into account air resistance, the ball takes longer to go up than to come down. T F [The average speed is less on the way down because energy is lost to air resistance.] Physics 53 Summer 2010 1

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3. A block of mass m is on a frictionless wedge, which is
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Unformatted text preview: being accelerated to the right as shown. The acceleration is of magnitude such that the block does not move relative to the wedge. a. In the inertial frame of the drawing, what force is doing work on the block to increase its speed? b. Find the acceleration a in terms of g and θ . c. In the non-inertial frame of the wedge, the block is at rest. What must be the direction of g eff in that frame? a. The horizontal component of the normal force. b. Horizontal forces: N sin = ma . Vertical forces: N cos = mg = . Eliminate N to ±nd a = g tan . c. The weight m g eff and the normal force N must cancel, so g eff must be opposte to N , i.e., perpendicular to the incline, inward. a Physics 53 Summer 2010 2...
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