A 34-pound crate is pushed across the floor by
a 30-pound horizontal force F1. Aside from
the pushing force and gravity F2, there is also
a 34-pound force F3 exerted upward on the
crate and a 20-pound frictional force F4
What kinds of work do the force F1, F2, F3,
F4 do, respectively?
1. +, 0, 0, 0
2. +, 0, 0, −
3. +, +, 0, 0
4. −, +, −, +
5. +, −, +, −
6. +, 0, +, 0
The answer is 2.) +,0,0,-
To determine the kind of work done by different forces, we need to understand the concept of work.
Work is done when a force causes an object to move over a distance. The work done by a force is given by the formula: Work = Force * Distance * cos(angle), where the angle is the measure of the angle between the force and the direction of motion.
Let's analyze each force one by one:
1. Force F1 (pushing force): This force is causing the crate to move horizontally across the floor. Since the force and displacement are in the same direction (angle = 0 degrees), the work done by Force F1 is positive (+).
2. Force F2 (gravity): This force acts vertically downward, but the crate is moving horizontally. As a result, the displacement and force act perpendicular to each other (angle = 90 degrees). The work done by Force F2 is zero (0) because cos(90) = 0.
3. Force F3 (upward force): This force is also acting vertically but is exerted upward on the crate. Since the crate is moving horizontally, the displacement and force are perpendicular to each other (angle = 90 degrees). The work done by Force F3 is zero (0) because cos(90) = 0.
4. Force F4 (frictional force): This force opposes the motion of the crate and acts horizontally. Since the force and displacement are in opposite directions (angle = 180 degrees), the work done by Force F4 is negative (-).
Based on this analysis, the kinds of work done by the forces are:
1. +, 0, 0, - (corresponding to the options provided, the correct answer is option 2: +, 0, 0, -).
So, Force F1 does positive work, Force F2 and Force F3 do no work (zero), and Force F4 does negative work.