The figure shows three forces applied to a trunk that moves leftward by 3.34 m over a frictionless floor. The force magnitudes are F1 = 5.39 N, F2 = 8.74 N, and F3 = 2.52 N, and the indicated angle is θ = 60°. ?
(a) During the displacement, what is the net work done on the trunk by the three applied forces, the gravitational force, and the normal force? (b) Is there a net transfer of energy to or from the trunk? (c) Does the kinetic energy of the trunk increase or decrease?
(a) During the displacement, what is the net work done on the trunk by the three applied forces, the gravitational force, and the normal force? (b) Is there a net transfer of energy to or from the trunk? (c) Does the kinetic energy of the trunk increase or decrease?
1 Answer
- Net work is
#3.4068J# , Gravitational force#=# Weight#=5.04906N# , normal force equals to zero . - Net transfer is to the trunk.
- Kinetic energy increases .
Explanation:
Part A
Work
Taking the left directions as negative and right as positive, we want the sum of the forces that are pointing horizontally. Hence,
Gravitational force (weight)
Hence
Since the trunk is not moving up or down, the forces pulling up and down must cancel each other.
Forces up
Forces down
Normal force is zero because the question says frictionless floor. For that to be possible, the normal force must be zero. See coefficient of static friction .
Part B
Energy transferred to the trunk because there is work done on the trunk (positive value).
Part C
Kinetic energy increases because you have positive work .
Other way to look at it is the net force is to the left, when there is a net force, there is acceleration .
Faster you go, higher your kinetic energy.
Cheers.