Some students want to calculate the work done by friction as an object with unknown mass moves along a straight line on a rough horizontal surface. The students have a force probe, a meterstick, and a stopwatch. Which of the following will allow the students to take the measurements needed to calculate the work done by friction?
A. Pulling the block at an unknown constant acceleration with the force probe for a measured time.
B. Pulling the block at an unknown constant speed with the force probe for a measured time.
C. Pulling the block at an unknown constant acceleration with the force probe for a measured distance.
D. Pulling the block at an unknown constant speed with the force probe for a measured distance.
If you pull the block with a constant speed, this means that there is no net acceleration, and hence the pulling force (force displayed on the force probe) equals the magnitude of the frictional force.
Hence, a constant speed would allow you to identify the magnitude of the frictional force.
Further, Work = Force * Distance along direction of Force
Hence, the distance must be measured.
The answer is D.
(Note that the work done would be negative since in this case the direction of displacement is exactly opposite to that of the frictional force)
To calculate the work done by friction, we need to measure the force of friction and the displacement of the object.
The force probe can be used to measure the force applied to the block.
The meterstick can be used to measure the displacement of the block.
The stopwatch can be used to measure the time taken for the block to move along the surface.
Option C, pulling the block at an unknown constant acceleration with the force probe for a measured distance, will provide the necessary measurements to calculate the work done by friction. By measuring the force applied with the force probe and the distance traveled with the meterstick, the students can determine the work done by friction using the formula W = Fd, where W is the work done, F is the force applied, and d is the distance traveled.
To calculate the work done by friction, we need to know two things: the force applied and the distance moved.
Option A: Pulling the block at an unknown constant acceleration with the force probe for a measured time.
This option only provides information about the force applied (measured by the force probe) and the time taken to move the block. It does not give any information about the distance moved. Therefore, we cannot calculate the work done by friction solely using this option.
Option B: Pulling the block at an unknown constant speed with the force probe for a measured time.
Similar to option A, this option only provides information about the force applied (measured by the force probe) and the time taken to move the block. It does not give any information about the distance moved. Hence, we cannot calculate the work done by friction using this option alone.
Option C: Pulling the block at an unknown constant acceleration with the force probe for a measured distance.
This option is useful because it provides information about the force applied (measured by the force probe) and the distance moved. With these measurements, we can calculate the work done by friction.
Option D: Pulling the block at an unknown constant speed with the force probe for a measured distance.
Similar to option C, this option also provides information about the force applied (measured by the force probe) and the distance moved. Therefore, we can calculate the work done by friction using this option as well.
Therefore, options C and D will allow the students to take the measurements needed to calculate the work done by friction.