Calculating Mass of a Car with KE of 1*10^6 J

[Lovely]

O.K . What is 1*10(6power)J mean. Do I further need to break this down in order to work the problem.
Problem: A car travleling 25 km/hour has Kinetic energy of 1*10(6power)J.
What is the mass of the car?
I've converted k/h to m/s

 

[Mathechyst]

O.K . What is 1*10(6power)J mean. Do I further need to break this down in order to work the problem.
Problem: A car travleling 25 km/hour has Kinetic energy of 1*10(6power)J.
What is the mass of the car?
I've converted k/h to m/s

Do you know what mass is in terms of velocity and energy?

Doug

 

[Lovely]

Do you know what mass is in terms of velocity and energy?

Doug

If I'm looking for mass am I suppose to know?

 

[Lovely]

If I'm looking for mass am I suppose to know?

No I do not know what mass is in terms of velocity and energy

 

[DirtyDan]

KE=\frac{1}{2}mv^2. So, if KE = 10^6, and v=25km/h or ~6.9m/s...
10000000/.5(6.9)^2=416666kg? Thats almost 300X the average mass of a car[/color]

Edited: Oops on Calculations, Thanks Mathechyst

 

[Mathechyst]

KE=\frac{1}{2}mv^2. So, if KE = 10^6, and v=25...
10000000/(312.5)=3200kg[/color]

It doesn't look like you accounted for the fact that the velocity is given in km/hr.

 

[DirtyDan]

Yeah, I've been editing it lol.. But now look, I checked it a couple of times. Is it meant to come out with non-sensical numbers?

 

[Mathechyst]

Yeah, I've been editing it lol.. But now look, I checked it a couple of times. Is it meant to come out with non-sensical numbers?

Since we're giving out the answer, we should show how it is solved:
<br /> m=\frac{2K}{v^2}=\frac{2\cdot1\cdot10^6 kg\cdot{m^2}}{s^2}\cdot\frac{hr^2}{25^2 km^2}\cdot\frac{3600^2 s^2}{hr^2}\cdot\frac{km^2}{1000^2 m^2}=\frac{2\cdot3600^2}{25^2}kg=41472kg<br />
Hmm. A 45.6 ton car. Still, it looks right to me. Let's do a back of the envelope calculation to see what we come up with. Suppose we have a 1000 kg (2200 lb) car going 25 km/hr.

<br /> \frac{mv^2}{2}=\frac{1000kg}{1}\cdot\frac{25^2 km^2}{hr^2}\cdot\frac{1000^2 m^2}{km^2}\cdot\frac{hr^2}{3600^2 s^2}=\frac{1000\cdot25^2\cdot1000^2 kg\cdot{m^2}}{s^2}=48225.3J<br />

Yes, I would say a million joules at 25km/hr is a bit much.

Doug

 

[Lovely]

Since we're giving out the answer, we should show how it is solved:
<br /> m=\frac{2K}{v^2}=\frac{2\cdot1\cdot10^6 kg\cdot{m^2}}{s^2}\cdot\frac{hr^2}{25^2 km^2}\cdot\frac{3600^2 s^2}{hr^2}\cdot\frac{km^2}{1000^2 m^2}=\frac{2\cdot3600^2}{25^2}kg=41472kg<br />
Hmm. A 9\frac{1}{2} ton car. Still, it looks right to me.

Doug

O.K Mathechyst I got completed lost. I didn't see were you converted k/m into m/s. I'm sorry but i guess I'm missing the whole concept

 

[Mathechyst]

O.K Mathechyst I got completed lost. I didn't see were you converted k/m into m/s. I'm sorry but i guess I'm missing the whole concept

I find it easier to include the units conversion along with the rest of the solution. It's just a matter of multiplying by 1. For example, to convert km/hr to km/s you multiply the km/hr by the number of hours in a second, namely 1/3600.

<br /> \frac{25 km}{hr}\cdot\frac{hr}{3600 s}=\frac{25 km}{3600 s}=\frac{1 km}{144 s}<br />

Notice how the hr units cancel? That's what you want to do. Cancel out the units you don't want and replace them with the units you do want. Now to convert km/s to m/s you just multiply km/s by the number of meters in a kilometer, so:

<br /> \frac{1 km}{144 s}\cdot\frac{1000 m}{km}=\frac{1000 m}{144 s}=6.94\frac{m}{s}<br />

See how the km[/tex] units cancelled?<br /> <br /> Doug

 

[Lovely]

I find it easier to include the units conversion along with the rest of the solution. It's just a matter of multiplying by 1. For example, to convert km/hr to km/s you multiply the km/hr by the number of hours in a second, namely 1/3600.

<br /> \frac{25 km}{hr}\cdot\frac{hr}{3600 s}=\frac{25 km}{3600 s}=\frac{1 km}{144 s}<br />

Notice how the hr units cancel? That's what you want to do. Cancel out the units you don't want and replace them with the units you do want. Now to convert km/s to m/s you just multiply km/s by the number of meters in a kilometer, so:

<br /> \frac{1 km}{144 s}\cdot\frac{1000 m}{km}=\frac{1000 m}{144 s}=6.94\frac{m}{s}<br />

See how the km[/tex] units cancelled?<br /> <br /> Doug

Thanks for the help. I have completed the activity. I appreciate you.<br /> <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":smile:" title="Smile :smile:" data-smilie="1"data-shortname=":smile:" />