Mythbusters jato rocket car mission accomplished

Physics

JATO Rocket Car: Myth or Reality?

Background:

The account of the JATO Rocket Car (Links to an external site.) is an early example of a viral anecdote from the 1990s. In this story, a man supposedly met his death in a spectacular manner after mounting a JATO unit (a rocket engine used to help heavy aircraft to take off) onto an ordinary automobile. Here is part of the story shared via email back then:

The Arizona Highway Patrol came upon a pile of smoldering metal embedded into the side of a cliff rising above the road at the apex of a curve. the [sic] wreckage resembled the site of an airplane crash, but it was a car. The type of car was unidentifiable at the scene. The lab finally figured out what it was and what had happened.

It seems that a guy had somehow gotten hold of a JATO unit (Jet Assisted Take Off – actually a solid fuel rocket) that is used to give heavy military transport planes an extra 'push' for taking off from short airfields. He had driven his Chevy Impala out into the desert and found a long, straight stretch of road. Then he attached the JATO unit to his car, jumped in, got up some speed, and fired off the JATO!

The facts as best could be determined, are that the operator of the 1967 Impala hit JATO ignition at a distance of approximately 3.0 miles from the crash site. This was established by the prominent scorched and melted asphalt at that location. The JATO, if operating properly, would have reached maximum thrust within five seconds, causing the Chevy to reach speeds well in excess of 350 MPH, continuing at full power for an additional 20–25 seconds. The driver, soon to be pilot, most likely would have experienced G-forces usually reserved for dog-fighting F-14 jocks under full afterburners, basically causing him to become insignificant for the remainder of the event. However, the automobile remained on the straight highway for about 2.5 miles (15–20 seconds) before the driver applied and completely melted the brakes, blowing the tires and leaving thick rubber marks on the road surface, then becoming airborne for an additional 1.4 miles and impacting the cliff face at a height of 125 feet, leaving a blackened crater 3 feet deep in the rock.

Your Assignment:

Use concepts of momentum and impulse, you are going to determine the plausibility of this story. You are to ignore other non-physics reasons to question whether or not someone could successfully attach such a rocket to an old sedan. Instead, you will focus your analysis on whether or not the speeds claimed in the story were possible.

Review the useful information provided below prior to beginning your assignment.

Rocket Motor, Solid Fuel, 15-KS-1000, JATO (Links to an external site.)

Rocket Motor.png

The motor produced 1,000 pounds of thrust for 15 seconds.

Loaded Weight: 143 lbs

1967 Chevrolet Impala

chevy impala.jpg

Shipping weight = 3500 lb

Additional Resources:

(16) Jato Rocket Car: Mission Accomplished? MythBusters Preview Ep. 18 - YouTube

Week 2 Assignment: Case Study - JATO Car

Student Name:

Record the values provided in the assignment and do the calculations. When two fields are provided for a quantity, the number part of the answer goes into the first field and the units in the second field.

Example:

How many centimeters in 1 meter:

100

cm

Useful unit conversions to change data from English units of force, weight in pounds, and speed in MPH to metric units of force in Newtons, mass in kilograms, and speed in meters/second:

1 pound = 4.448 Newtons

1 pound of weight requires 0.4536 kg of mass

1 MPH = 0.44704 m/s

1. Use the estimated thrust of a JATO rocket and the time it fires to predict the change in momentum of the car from the time the rocket starts until it stops. You can use the time given in the story or the shorter time listed in the properties of the 15-KS-1000 solid fuel rocket.

Formula: Change in Momentum = Force x Time

Rocket Thrust in units of Newtons

Time thrust is applied

Impulse

The car’s change in momentum

2. Given the mass of the car plus rocket, use the change in momentum to calculate the change in speed. Formula:

Mass of car in kilograms

Mass of rocket in kilograms

Total mass of car and rocket in kilograms

Change in speed of car (in m/s)

3. Convert this speed from meters/second to MPH. Then add this to the alleged initial speed when the rocket was fired (assume 50 MPH).

Change in speed of car (in MPH)

Final speed of car after adding initial speed

4. In the field below, discuss one other potentially questionable claim of the