# Hollywood Physics #1: xXx

Introduction

Chase scenes: what would Hollywood be without them?  But...how accurate are the physics involved? And, if you had to catch up to your cousin who forgot his sandwich in your car, after he jumped on his speeding train to the Rocky Mountains, would you really be able to catch up with him at the next station, the way they do in Hollywood?

In the finale of the movie xXx, our hero, Xander Cage (played by Vin Diesel), has to stop a boat racing along a river before it reaches the city of Prague, Czechia, and releases a toxic gas (called “Silent Night”) that will kill 1.2 million people.  What does he do? Chase it down in a car, of course!

In this Webquest, based on Adam Weiner's book, Don't Try This at Home, you'll practice estimating and calculating distances, speeds, and times involved in Xander's chase--and determine if the physics are real, or just Hollywood stuff.

Good luck!

Watch the movie clip of the boat chase scene in xXx, and gather as much data as you can about the speeds, times, and distances involved in Xander’s problem in order to answer the questions below on your handout.  The chase scene begins at 1:37:30.

Movie Data

 Question Answer How long will it take the boat to reach the town? How fast is the boat traveling? How many minutes are left when Samuel L. Jackson’s character gives the order to launch an airstrike to blow up the boat? How many miles must the car travel away from the river? When Xander lands on the boat, how many minutes are left before military planes blow up the boat? 6. After the boat arms itself and Samuel L. Jackson’s troops arrive at the bridge, how many minutes are left until the planes blow up the boat? 7. When Xander finally figures out how he is going to stop the boat, how many seconds are left before the planes blow up the boat?

In the space at the bottom of your handout, draw a diagram of the boat’s path on the river and the car’s path traveling alongside it, based on what you saw in the movie.  Label the starting point of the boat “Point A,” the beginning of the detour “Point B,” the end of the detour “Point C,” and the city of Prague “Point D.”  (Hint: use the image of the GPS in the movie to help you with the diagram.)

Use this video on YouTube to review the GUESS Method for solving word problems. Then, apply the GUESS Method to word problems based on the movie.  Use your data --the distances, speeds, and times GIVEN in the movie --  and keep track of your answers for each problem, as you will need new values to solve the new problems as the chase continues!

xXx Problem Sets

Use the data and diagram you created on the previous page to help you create and solve the problems below.  Use the equations distance = speed x time and speed = distance/time to help you.

1. Assume the boat travels at a constant speed the entire time it is in the river.  What is the distance between Point A (where the boat is launched) and Point D (Prague, where it will release the poison gas)?

2. If the car starts chasing the boat after the boat has a 3-minute head start, and catches up to the boat after 7 minutes, what is the total distance the car has to travel? To simplify the problem, assume the car travels the same distance that the boat covers in 10 minutes.

If the car has to cover this same distance in only 7 minutes, what is its average speed during the chase?

3. At one point, the road curves away from the river and Xander’s car has to take a detour of an extra ________ miles.  At what average speed does the car have to travel to meet the boat when the road crosses the river again, after the town of Davale?  Assume that the car takes 12 minutes to catch up to the boat again.

4. When Xander lands on the boat, there are only _________ minutes left until the bombs detonate.  How far away is he from the city of Prague at that moment?

5. After Xander lands on the boat, notice that Yelena (the female sidekick/love interest) speeds up the car to reach the last bridge before Xander does.  Let’s say she reaches the bridge 30 seconds before he does.  In other words, she travels the distance from problem #4 in 2.5 minutes, not 3.  What is her average speed during that part of the drive?

6. The fighter jets only have 22 minutes total to reach the boat and try to blow it up before it reaches the center of the town.  If the average speed of the fighter jets is 900 miles per hour (Mach 1.17), how far away is the airbase from the city of Prague when they first take off?

7. When Xander finally drives the boat into the bottom of the river, how fast is he going when he is thrown from the boat into the water?

8. Look back at your problem-solving in this exercise. Which results are the most realistic, based on what you know about how fast cars, boats, and planes can travel?  In which situations did the movie rely on “fake” or “Hollywood” physics? Explain your answer.

Use this video to review how to graph speed over time.  Then, plot Xander's velocity for as many different minutes as you can, and connect them with straight line segments.  This will help you understand how Xander's speed changed -- or how he accelerated over the course of the chase. The steeper the line, the greater the acceleration.  Are these values realistic?

Based on the movie data and your problem-solving, plot the speed of the boat AND the speed of Xander’s car for each of the 30 minutes of the boat chase on the graph below.  Label the x-axis t  for time in minutes, and the y-axis s for speed in miles per hour.  (Hint: you will be drawing one line for the boat, and several line segments for the car.)

Evaluation

Now that you've analyzed Xander's chase, create a NEW chase scene that is more realistic.

How fast is the boat traveling?

When does Xander begin chasing it?

How long does it take him to catch up?

How far away from Prague is the boat, in order for Xander to still be able to save the day?

Conclusion

Congratulations!

Hollywood may just have to hire you as a physics consultant.  Stay tuned for more Hollywood Physics Problems!

Credits