Unit 4 Progress Check: MCQ Part B

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Answer explanation

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Answer explanation

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Answer explanation

The initial kinetic energy of the block is equal the total mechanical energy of the block-spring system. Therefore, whenever one must determine the spring potential energy of the block-spring system at different distances in which the spring is compressed, one must take the total mechanical energy of the spring-block system (54J) and subtract the kinetic energy of the block at each distance represented in the graph. This is the only data set in which the spring-potential energy of the system and the kinetic energy of the block are equal to the total mechanical energy of the system.

• A graph of the force exerted on the object as a function of time is required to determine the work done on the object.

An experiment is conducted such that an applied force is exerted on an object as it travels across a horizontal surface with a constant speed. A graph of the applied force exerted on the object as a function of the object’s distance traveled is shown. Which of the following claims is correct regarding the work done on the object by the applied force from one data point to the next data point?

• The work done remains nearly constant for all displacements.

• The work done increases for all displacements.

• The work done decreases for all displacements.

• The work done is zero for all displacements because the speed of the object remains constant.

Answer explanation

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Answer explanation

The mechanical energy of the block is equal to the kinetic energy of the block at all locations along the block’s path. When the block travels along the horizontal path at the bottom of the ramp, the block has its maximum kinetic energy. As the block travels up the ramp, Earth exerts a downward force doing negative work on the block, decreasing the block’s kinetic energy. The mechanical energy of the block-Earth system is equal to the sum of the kinetic energy of the block and the gravitational potential energy of the block-Earth system. The block-Earth system is a closed system, because no external forces are exerted on the system that can change the mechanical energy of the system. Therefore, the mechanical energy of the block-Earth system remains constant at all locations of the block.