• Support PF! Buy your school textbooks, materials and every day products Here!

Final speed with mass, initial velocity, force, displacement

  • Thread starter TDizzl
  • Start date
  • #1
12
0

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:

Answers and Replies

  • #2
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,666

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?
 
  • #3
ehild
Homework Helper
15,427
1,827

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?
 
  • #4
12
0
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
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.
 

Attachments

  • #5
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,798
1,666

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
 
  • #6
12
0
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
 
  • #7
ehild
Homework Helper
15,427
1,827
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?
 
  • #8
12
0
The answer is correct as ms-1
 

Related Threads on Final speed with mass, initial velocity, force, displacement

Replies
4
Views
15K
Replies
4
Views
6K
Replies
2
Views
650
Replies
5
Views
31K
  • Last Post
Replies
7
Views
2K
Replies
3
Views
10K
Replies
10
Views
804
Top