Kinetic Energy and Work Energy Theorem

In summary, a 65kg bicyclist riding a 8.8kg bicycle at a speed of 14m/s requires 7232.4 joules of work from the brakes to bring them to a stop. Using kinematics, the bicycle will travel approximately 56 meters in 4 seconds before coming to a complete stop. The magnitude of the braking force would be equal to the average acceleration multiplied by the time it takes to stop.
  • #1
just.karl
64
0
A 65kg bicyclist rides his 8.8kg bicycle with a speed of 14m/s. (a) How much work must be done by the brakes to bring the bike and rider to a stop? (b) How far does the bicycle travel if it takes 4.0s to come to rest? (c) What is the magnitude of the braking force?


So for part (a) the equation I would use is W=1/2mv_f^2 - 1/2mv_i^2 correct? Which then I get for an answer is 7232.4=W which means 7232.4 Newtons?

For part (b) I know the work that it takes to stop the bicyclist and bicycle but what I'm confused on what equation I would need to use to figure that out.


thanks
 
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  • #2
For part (a), work is the change in kinetic energy, which you did good...but what are the units for work? If it is equal to KEf - KEi, what does that tell you?

For part (b), think kinematics.
 
  • #3
O yeah it's joules for part (a)

For part (b) it would be just velocity/time = -average acceleration then I would just multiply that by the amount of time? correct?
 

Related to Kinetic Energy and Work Energy Theorem

1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion. It is a form of energy that an object has by virtue of its movement, and it is directly proportional to the mass and velocity of the object.

2. How is kinetic energy calculated?

Kinetic energy is calculated using the formula KE = 1/2 * m * v^2, where m is the mass of the object and v is its velocity. This means that the greater the mass and velocity of an object, the more kinetic energy it has.

3. What is the Work Energy Theorem?

The Work Energy Theorem states that the net work done on an object is equal to its change in kinetic energy. In other words, the work done on an object by all the forces acting on it will result in a change in its kinetic energy.

4. How does kinetic energy relate to potential energy?

Kinetic energy and potential energy are two forms of energy that an object can possess. Kinetic energy is the energy an object has due to its motion, while potential energy is the energy an object has due to its position or state. They are both interrelated and can be converted into one another.

5. Can kinetic energy be lost or gained?

Yes, kinetic energy can be lost or gained. When an object is in motion, it possesses kinetic energy. If it hits another object and comes to a stop, its kinetic energy is converted into other forms, such as sound or heat. Similarly, an object can gain kinetic energy when a force is applied to it, causing it to accelerate.

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