Dissipated Heat in Joules for Braking Motor with Given Parameters

In summary, the question asks for the amount of heat in joules dissipated in the brakes when the power to a motor is shut off while running at 3000 rpm and a brake is applied. To solve this, we need to determine the moment of inertia of the motor armature, which is equal to \frac{1}{2}mr^2. Using the given values of mass (250 kg) and diameter (30 cm, or 0.3 m), we can calculate the moment of inertia to be 3.375 kgm^2. Then, we convert 3000 rpm to angular speed (314.16 rad/s) and plug in the values to the equation for kinetic energy, \frac{1
  • #1
Dangousity
6
0

Homework Statement



Motor running, brakes applied. how much heat in joules will be dissipated?
mass 250 kg
diameter 30 cm
3000 rpm
torque 120 N-m




Homework Equations



W=1/2 *I *w2

The Attempt at a Solution



I keep going the route of:

(1)/(2)*250*.3*315

1*125*.3*315

125*.3*315

37.5*315

11812.5 J

Can anyone show me what I am doing wrong?
 
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  • #2
You will have to explain the question. There is insufficient information here. Give us the complete wording of the question.

AM
 
  • #3
If the power to the motor is shut off while the motor is running at 3000 rpm, and a brake is applyed, how much heat in Joules will be dissipated in the brakes in order to bring the motor to a stop.

Figuring W=1/2*I*w2

Sorry about the messy paper
 

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  • #4
Dangousity said:
If the power to the motor is shut off while the motor is running at 3000 rpm, and a brake is applyed, how much heat in Joules will be dissipated in the brakes in order to bring the motor to a stop.

Figuring W=1/2*I*w2

Sorry about the messy paper
Ok. We needed the information in the attached paper about the design of the motor in order to determine the moment of inertia. What is the moment of inertia of the motor armature then?

You seem to have the right idea here. The energy dissipated in the brake is equal to the kinetic energy of the rotating motor which is [itex]\frac{1}{2}I\omega^2[/itex]. You just have to determine I and convert 3000 rpm into angular speed and then plug in the values (using appropriate units, of course).

AM
 
  • #5
Andrew Mason said:
You just have to determine I and convert 3000 rpm into angular speed and then plug in the values (using appropriate units, of course).

AM

Accord to my instruction "I" is I=Mr2
M=250kg
r2=225cm = 2.25 meter

Is this correct?
 
  • #6
Dangousity said:
Accord to my instruction "I" is I=Mr2
M=250kg
r2=225cm = 2.25 meter

Is this correct?
No. You have to treat the armature as a solid cylinder. Look up the moment of inertia of a solid cylinder.

AM
 
  • #7
Andrew Mason said:
No. You have to treat the armature as a solid cylinder.

AM

So I = 1/2 m r2 instead.
 

Related to Dissipated Heat in Joules for Braking Motor with Given Parameters

1. What is "breaking heat"?

Breaking heat refers to the amount of thermal energy required to break the bonds between atoms or molecules in a substance. It is measured in joules (J) and is often used to describe the energy needed to initiate a chemical reaction or phase change.

2. How is breaking heat in joules determined?

Breaking heat is typically determined through experiments where the amount of energy needed to break the bonds in a substance is measured. This can be done using techniques such as calorimetry, where the change in temperature of a substance is used to calculate the amount of energy released or absorbed during a reaction.

3. What factors can affect the breaking heat of a substance?

The breaking heat of a substance can be affected by various factors such as the strength and type of bonds between atoms or molecules, the temperature and pressure of the environment, and the presence of catalysts or inhibitors that can either increase or decrease the energy required to break bonds.

4. How is breaking heat related to the stability of a substance?

The higher the breaking heat of a substance, the more stable it is. This is because substances with strong bonds require more energy to break, making them less likely to undergo chemical reactions or phase changes. On the other hand, substances with weak bonds have a lower breaking heat and are more reactive and less stable.

5. Can breaking heat in joules be changed?

Yes, the breaking heat of a substance can be changed by altering the factors that affect it, such as temperature, pressure, and the presence of catalysts or inhibitors. Additionally, the breaking heat of a substance can also be affected by the physical state of the substance, as different states (solid, liquid, gas) have different breaking heat values.

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