Topic: Physics question | The Yeshiva World

This topic has 12 replies, 4 voices, and was last updated 9 years, 8 months ago by 000646.

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April 9, 2014 10:32 pm at 10:32 pm #612558

000646
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I am trying to learn basic Physics and am learning about applying Newton’s Laws in 2 and 3 dimensional motion. I really know anyone who knows this stuff and I know that a lot of smart people read the stuff here sometimes.. I am hoping maybe someone can help me out:

Did I do this correctly? If not where am I wrong?

Thanks!!

April 9, 2014 11:45 pm at 11:45 pm #1011372

Epis
Participant

What is the mass of you car? That is a major factor. According to netons 3rd law, every thing has opposite and equal force. The reason why you don’t fall through the floor is because of this opposite and equal force or better known as the NORMAL FORCE. To fid your normal force, you multiply your mass*gravity (mg). So that is what you are missing the mass of the car.

April 10, 2014 12:16 am at 12:16 am #1011373

000646
Participant

epis,

Right?

April 10, 2014 1:15 am at 1:15 am #1011374

–
Participant

I got 27.3 MPH but that’s because I started out by converting everything to SI units. I think your error is in approximation too early in the equation.

April 10, 2014 1:27 am at 1:27 am #1011375

Epis
Participant

Your righ I over thought the example.

April 10, 2014 1:28 am at 1:28 am #1011376

000646
Participant

Dash,

I’m not sure I understand what you mean…

April 10, 2014 1:51 am at 1:51 am #1011377

Epis
Participant

A 4.20*10^3-kg rocket takes off from the moon where the acceleration due to gravity is 1.60 m/s^2 by exhausting 8.20 kg of gas per second at a speed of 2.20 103 m/s. Determine the acceleration of the rocket.

April 10, 2014 3:54 am at 3:54 am #1011378

000646
Participant

If you mean it went from 2.2 m/s to 103 m/s while it burned gas for 1 second. Then it’s accelerating at 100.8 m/s. I’m not sure I understood your question though

April 10, 2014 8:12 am at 8:12 am #1011379

–
Participant

I’m not sure I understand what you mean…

I went back and looked at what you did and came up with the following

April 10, 2014 1:06 pm at 1:06 pm #1011380

Epis
Participant

000646, it is supose to be 2.20*10^3 m/s

April 10, 2014 1:39 pm at 1:39 pm #1011381

Avram in MD
Participant

Dash is correct – you have to make sure all of your units line up, which is best done by showing all work.

Newton’s Second Law: F = ma

The gravitational acceleration is g = 9.8 m/s

Centripetal acceleration is a = v^2/r

So to keep that car on track, you want to balance the centripetal acceleration with gravitational acceleration, so: 9.8 = v^2/r

Your r is known: 50ft, which is 15.24m, so v^2 = 9.8 * 15.24, and v = sqrt(9.8 * 15.24) = 12.22 m/s.

Converting 12.22 m/s into mph and you get 27.3.

April 10, 2014 2:28 pm at 2:28 pm #1011382

Avram in MD
Participant

Whoops, in my above post, the units for acceleration should be m/s^2, not m/s 🙂

April 10, 2014 2:33 pm at 2:33 pm #1011383

000646
Participant

Dash and Avram in Md

Thanks!
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