4. A physics teacher asks their students to conduct an experiment in which they pull a block up an incline with a force sensor. The students are supposed to change the mass of the block and measure the force
of friction acting on the block. Which is the independent variable?
a. mass of the block
c. same incline
b. force of friction
d. same force sensor
e time

Askydiver weighing 140 lb (including equipment) falls vertically downward from an altitude of 19,000 ft and opens the parachute after 18 s of free fall. assume that the force of air resistance, which is directed opposite to the velocity, is of magnitude 0.55|v| when the parachute is closed and is of magnitude 14|v| when the parachute is open, where the velocity v is measured in ft/s. assume that acceleration due to gravity has magnitude 32 ft/s/s; remember that weight is the product of mass and gravitational acceleration. (a) find the speed of the skydiver when the parachute opens. (b) find the distance fallen before the parachute opens. (c) what is the limiting velocity vl after the parachute opens? (d) determine how long the sky diver is in the air after the parachute opens. (e) plot the graph of velocity versus time from the beginning of the fall until the skydiver reaches the ground.

Iwill give brainliest if you answer right : )

Select the correct answer. what does the process of natural selection involve?