(3)
(4) It is proportional to the work and the square of the speed of the object.
Test and analysis: (1) According to the calculation formula of work, as long as the force f remains unchanged, the relationship between work and speed change can be qualitatively judged by changing the distance of force movement, so there is no need to measure gravity.
(2) As long as the resultant force is constant, there is no need to balance friction, and there is friction every time, then the resultant force is certain.
(3) To find out the qualitative relationship, it is best to draw the image as a straight line and find out the linear relationship. If the drawn image is a curve, it is impossible to judge whether it is a quadratic function, a cubic function or an inverse proportional function, nor can it judge the relationship. Analyzing the data, I found that the image with them is a straight line, so I can draw a picture according to the data.
(4) From the image, we can find that it is an inclined straight line, which is proportional to the origin. And then what? It is proportional to work, so the relationship between work and speed change is that work is proportional to the square of object speed.