# KE-1/2mv^2 physics question

hi I am new and new to physics i am have alot of trouble with this problem

mass =1.3kg
41.5J
how do i get the velocity

so far i have it wrote like this
41.5J=1/2(1.3kg)(v)^2

but dont know how else to do plz help thanks ron

The equation KE=1/2mv^2 says that the kinetic energy is equal to half of the mass of the object times the object's velocity squared. So you need to solve for velocity (v). Isolate the v variable using algebra (try to get v by itself on one side of the equation).

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KE=1/2mv^2
41,5J=1/2*1,3*v^2
41,5J/(1/2*1,3)=1/2*1,3*v^2/1/2*1,3
63,8=v^2
sqrt(63,8)=v
v=7,98 m/s

Integral
Staff Emeritus
Gold Member
You will find that it is easier to do your algebra BEFORE plugging in the numbers. You have

$$\mbox{KE} = \frac 1 2 m v^2$$
then
$$2 \mbox{KE} = m v^2$$
then

$$2 \frac {\mbox{KE}} m = v^2$$

so

$$v = \sqrt { 2 \frac {\mbox{KE}} m }$$

Now you can substitute in your numbers and arrive at the numeric solution.

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thank you for the help i have been out of school 24 years and this is my last semester for my degree thanks ron