At this instant, MJ’s acceleration is pointed upward, since that’s towards the center of the circle. In order for the net force to be equal to mass times acceleration, the upward-pulling tension force must be greater than the downward-pulling gravitational force.
We can write this down as the following equation. (This is a scalar equation since all the forces are along a vertical axis.)
Since this is a scalar equation, the gravitational force will be negative, meaning downward movement. From this, I can solve for the tension force pulling on MJ, and thus the force she needs to exert to hang on to the web.
But that still leaves the question: Could she actually hang on? For that, we are going to need some numerical values.
Estimations From the Trailer
Although the shot of Spidey and MJ swinging through the city looks cool, it’s not really set up for a physics problem. I would like to see a nice stable view from the side with something nearby to help me determine the distance scale. But no—instead we get something that is visually appealing, seemingly shot with the camera beneath the arc of the swing.
Fine. I guess I will just have to make some rough estimates. But don’t worry, I’m going to put all the calculations here so that you can change the values if you don’t like my guesses.
Really, there are just three things I need to estimate: the length of the web during the swing, the speed of MJ at the bottom of the swing, and MJ’s mass. Finding the mass is the easiest. I can just look up the measurements of Zendaya Coleman, who plays MJ. I’ll go with a mass of 59 kilograms, an estimate on a celebrity biography page—this might not be accurate, but in the end, this value doesn’t matter too much.