What is the velocity of the body

[nmegabyte]

The only force acting on a 3.4 kg body as it moves along the positive x-axis has an x component Fx = - 6x N, where x is in meters. The velocity of the body at x = 3.0 m is 8.0 m/s.

a) What is the velocity of the body at x = 4.0 m? m/s

(b) At what positive value of x will the body have a velocity of 5.0 m/s?
i have some kinda idea but it may not be clear
so i started with using a Formula for work since its moving along positive x direction
W=Fd cos(angle)
and kinetic energy is
K=1/2mv^2
thats all i can think off for the beginning
Plz just give me some hint how to combine these 2 formulas since angle between force and direction is 180 it will be cos180

 

[rock.freak667]

Your force is varying with x.

So if the only force acting is F_x= 6x, can you use Newton's second law to find an expression for velocity?

(Hint: dv/dt = dv/dx * dx/dt)

 

[nmegabyte]

still don't get it

 

[rock.freak667]

still don't get it

F= ma

-6x = ma