## View Poll Results: What is answer the following question?

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# Thread: Help in speed problem please

1. hello i need help in solving this
Q)If the speed of a vehicle increases by 2 m/s,its kinetic energy is doubled,then original speed of the vehicle is
a)(sqrt of 2 )+1 m/s

b)2(sqrt of 2 -1)m/s
c)2(sqrt of 2 + 1 )m/s
d)sqrt of 2 (sqrt of 2 + 1)m/s
sqrt is square root of

2.

3. What have you got so far?

4. I found the answer as 2(sqrt of 2 + 1 )m/s i just want you to cross check it

5. Originally Posted by Rajnish Kaushik
I found the answer as 2(sqrt of 2 + 1 )m/s
Not useful.
HOW did you arrive at that answer?

6. i just used the identity 1/2*m*(v+2)^2 = 1/2*m*v^2 * 2

7. 1/2*m*(v+2)^2 = 1/2*m*v^2 * 2 ie KE=PE

8. And did you check it?
E.g.:
2(sqrt of 2 + 1 )m/s = (2(1.414+1) = 4.828 m/ s,
Square that = 23.3.

New value = 6.828 (i.e. adding 2 m/ sec).
6.8282 = 46.6.

46.6/23.3 = 2.

Confirmed.

9. Originally Posted by Dywyddyr
And did you check it?
E.g.:
2(sqrt of 2 + 1 )m/s = (2(1.414+1) = 4.828 m/ s,
Square that = 23.3.

New value = 6.828 (i.e. adding 2 m/ sec).
6.8282 = 46.6.

46.6/23.3 = 2.

Confirmed.
So i was right yeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeee

10. I've always found that plugging in the numbers and actually calculating them helps.

11. Originally Posted by Dywyddyr
I've always found that plugging in the numbers and actually calculating them helps.