# What is the force needed to stop an 8,000lb tractor moving at 5mph in one foot?

• Eric Ahlvin
In summary, the conversation discusses the calculation of force required to stop an 8,000lb tractor moving at a speed of 5mph in a distance of 1 foot. The kinetic energy equation is used to calculate the force, which is found to be 1501.7 lbs. However, there is some confusion regarding the use of SI units and it is suggested to redo the calculation without considering SI units.
Eric Ahlvin
I have a situation where I need to figure how much force it will take to stop an 8,000lb tractormoving at a max speed of 5mph in somewhere around a foot. It will not be an impact stop as there is nothing for it to hit but rather a heavy brake stop. It has been quite some time since I have dealt with kinetic energy equations. Can someone check my work on this?

K=1/2mv^2
m=8,000lb x 0.0310809502 lbs/slug = 248.64slugs
v = 5m/hr x 5280ft/mile x 1hr/60min x 1min/60sec = 7.33 ft/sec

K=0.5 * 248.64slugs * 7.33^2

K= 6,680 ftlbs

where F=K/d and d=1ft

F= 6680Newtons and 1 Newton = 0.224808943 pounds force

so F= 1501.7 lbs

If someone could verify this that would be very much appreciated

Sorry, I see this was not the place to put this, but I also do not see how to delete it...

It makes a great homework problem. Leave it right where it is and don't worry.
Eric Ahlvin said:
K= 6,680 ftlbs
This is good.
Eric Ahlvin said:
where F=K/d and d=1ft
This is good.
Eric Ahlvin said:
F= 6680Newtons and 1 Newton = 0.224808943 pounds force
What are you trying to do dragging in SI units? NOT good.
Eric Ahlvin said:
so F= 1501.7 lbs
The SI conversion messed this up for you. Try it again without worrying about SI.

## 1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity.

## 2. How is kinetic energy calculated?

Kinetic energy can be calculated using the formula KE = 1/2 * m * v^2, where m is the mass of the object and v is its velocity.

## 3. What are the units of kinetic energy?

The SI unit of kinetic energy is joule (J), but it can also be expressed in other units such as kilogram-meter squared per second squared (kg*m^2/s^2) or foot-pound (ft-lb).

## 4. How does kinetic energy relate to potential energy?

Kinetic energy and potential energy are two forms of mechanical energy. Kinetic energy is the energy of motion, while potential energy is the energy an object has due to its position or state. The sum of kinetic and potential energy is known as total mechanical energy.

## 5. What factors affect an object's kinetic energy?

The factors that affect an object's kinetic energy are its mass and velocity. A heavier object or an object with a greater velocity will have a higher kinetic energy compared to a lighter object or an object with a lower velocity.

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