bascially, i'm 100% sure i understod the wording of the question, below, can you please check though i confirm i interpretted right, thnx buddies

## Homework Statement

the kinetic energy, E joules, of an object moving with a speed v m/s, is directly proportional to v^2.

the kinetic energy of the object is 15 480 joules when its speed is 6 m/s.

a) find a formula for E in terms of v

none

## The Attempt at a Solution

Ev (proportional sign) v^2
Ev = kv^2
15480 x 6 = k x 6^2
92 880 = k x 36
k = 2580

Ev = 2580 x v^2
E = 2580v

thnx for the help

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Hootenanny
Staff Emeritus
Gold Member
I am curious as to how you came to this conclusion;
Ev (proportional sign) v^2

that where i get confused, i kinda thought the question meant that the kin energy times the speed is proportional to the speed squared

either that or i'm totally confused

thnx

Hootenanny
Staff Emeritus
Gold Member
that where i get confused, i kinda thought the question meant that the kin energy times the speed is proportional to the speed squared

either that or i'm totally confused

thnx
No, not quite. The statement means simply that $E\propto v^2$.

Last edited:
o rite, i see, thnx for clearing that up, but isn't it E proptional to v squared?

thnx buddy

Gokul43201
Staff Emeritus
Gold Member
The trick (if I understand the source of your confusion) is to learn to partition the sentence correctly.
the kinetic energy, E joules, of an object moving with a speed v m/s, is directly proportional to v^2.
Try to throw away all non-essential details and extract the thrust of the statement, i.e., some property of some object is proportional to some other property.

Then you can keep track of the details separately...
Some property = KE
some object = "object moving with a speed v"
some other property = v^2

The upshot of this is that one property is proportional to another, namely, KE prop v^2

Perhaps it would help if you read the sentence as though it were written this way: the kinetic energy, E joules, (of an object moving with a speed v m/s) is directly proportional to v^2.

Hootenanny
Staff Emeritus
Gold Member
o rite, i see, thnx for clearing that up, but isn't it E proptional to v squared?

thnx buddy
Sorry, that was a typo. Now corrected

The trick (if I understand the source of your confusion) is to learn to partition the sentence correctly.
Try to throw away all non-essential details and extract the thrust of the statement, i.e., some property of some object is proportional to some other property.

Then you can keep track of the details separately...
Some property = KE
some object = "object moving with a speed v"
some other property = v^2

The upshot of this is that one property is proportional to another, namely, KE prop v^2

Perhaps it would help if you read the sentence as though it were written this way: the kinetic energy, E joules, (of an object moving with a speed v m/s) is directly proportional to v^2.

o rite eyh that'll be where i was going wrong lol, thnx for that, i understadn now :D