Final speed with mass, initial velocity, force, displacement

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Homework Help Overview

The discussion revolves around a physics problem involving a 1000kg car initially moving at 25 m/s, which is subjected to a net force of 200N acting in the opposite direction over a distance of 300m. Participants are tasked with finding the new speed of the car after the force has acted.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants attempt to use the Kinetic Energy equation and the equation of motion v² = u² + 2as. There are questions regarding the calculations and the interpretation of the results, particularly concerning the direction of the force and its effect on speed.

Discussion Status

The discussion includes various attempts to clarify the calculations and the assumptions made regarding the force acting on the car. Some participants suggest checking the original data and the units used, while others provide insights into the work-energy principle and the implications of negative acceleration.

Contextual Notes

There is a mention of a multiple-choice format for the problem, and some participants express confusion over the units of speed and the nature of the force acting on the car.

TDizzl
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Homework Statement


A 1000kg car is moving at 25ms when a net force of 200N acts to slow the car. This force acts while the car moves through a distance of 300m. Find the new speed.

Homework Equations


Kinetic Energy equation
v2=u2+2as

The Attempt at a Solution


Attempted the use of Kinetic Energy equation and v2=u2+2as
However the answer I get is 27.4 when the correct answer is 22.5
 
Last edited:
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TDizzl said:

Homework Statement


A 1000kg car is moving at 25ms when a net force of 200N acts to slow the car. This force acts while the car moves through a distance of 300m. Find the new speed.

Homework Equations


Unknown

The Attempt at a Solution


Attempted the use of Kinetic Energy equation and v2=u2+2as
However the answer I get is 27.4 when the correct answer is 22.5
Why don't you show us your calculations?
 
TDizzl said:

Homework Statement


A 1000kg car is moving at 25ms when a net force of 200N acts to slow the car. This force acts while the car moves through a distance of 300m. Find the new speed.

Homework Equations


Unknown

The Attempt at a Solution


Attempted the use of Kinetic Energy equation and v2=u2+2as
However the answer I get is 27.4 when the correct answer is 22.5
Are the relevant equations unknown to you? How did you solve the problem then?
You result is correct with the data you gave. Check if they are the same given in the original text. And do not forget the unit next time. What is the unit of the speed? Is it really ms?
 
SteamKing said:
Why don't you show us your calculations?
W=Fd
=200*300
=60000
60000=½*1000*v2-½*1000*252
=500v2-312500
372500 = 500v2
v2=745
v=27.3
ehild said:
Are the relevant equations unknown to you? How did you solve the problem then?
You result is correct with the data you gave. Check if they are the same given in the original text. And do not forget the unit next time. What is the unit of the speed? Is it really ms?
Yea see for yourself, its a multiple choice question. And I changed the original post so it makes some sense.
 

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TDizzl said:

Homework Statement


A 1000kg car is moving at 25ms when a net force of 200N acts to slow the car. This force acts while the car moves through a distance of 300m. Find the new speed.

Homework Equations


Kinetic Energy equation
v2=u2+2as

The Attempt at a Solution


Attempted the use of Kinetic Energy equation and v2=u2+2as
However the answer I get is 27.4 when the correct answer is 22.5
The force of 200 N is acting to slow the car, which is traveling initially at 25 m/s. If the force is acting to slow the car, it makes little sense to say that the car is going to speed up to 27.4 m/s. :oops:

Care to try again? I suggest you use F = ma here, in addition to v2=u2+2as
 
SteamKing said:
The force of 200 N is acting to slow the car, which is traveling initially at 25 m/s. If the force is acting to slow the car, it makes little sense to say that the car is going to speed up to 27.4 m/s. :oops:

Care to try again? I suggest you use F = ma here, in addition to v2=u2+2as
Thanks, I managed to get the answer, all I done was
27.5-25=2.5
25-2.5=22.5
 
TDizzl said:
W=Fd
=200*300
=60000
60000=½*1000*v2-½*1000*252
=500v2-312500
372500 = 500v2
v2=745
v=27.3

Yea see for yourself, its a multiple choice question. And I changed the original post so it makes some sense.

As the car slows down, the acceleration is negative. The force is opposite to velocity and displacement, so the work W is negative. You should have written W=Fd=-200*300= -60000 = 1/2mv2-1/2 m u2.

You changed the original post by changing the unit of speed from ms-1 to ms. Is it correct?
 
The answer is correct as ms-1
 

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