How far will the eraser slide with a compressed spring and friction force?

[F.B]

A student uses a compressed spring of force constant 22 N/m to shoot a 0.0075 kg eraser across a desk. The magnitude of the force of friction on the eraser is 0.042 N. How far along the horizontal desk will the eraser slide if the spring is initially compressed 3.5 cm. Use the law of conservation of energy.

i think you have to find acceleration first but it doesn't make sense when i do it. I end up 97 m/s.

Heres what i did.

Fnet=Fe-Ff
But i think that's wrong.

so can anyone please help me.

 

[Fermat]

What work is done by the spring as it decompresses by 3.5 cm ?
That work done/energy lost is transferred to the eraser as kinetic energy.
Use that to find the initial velocity of the eraser.

The friction force is what provides the deceleration.

 

[runicle]

fnet = fapp + f
force of friction is opposite to f so
fnet = fapp + ( - f)

ma= ... you know (hint look below an your units)

if not

force is known as kg*m/sy*2 (y* means to the power of) and by the way don't forget to convert your units to standard SI untis

 

[F.B]

if i do Ee=Ek i get 1.89 m/s as speed. What do i do now with it.

Whats Fapp you get figure that out unless its a constant velocity

 

[runicle]

Fapp is "applied force" and use the 6 basic equations to find your displacement

 

[F.B]

I know that Fapp is the applied force but there isn't an applied force in this question.

 

[Fermat]

if i do Ee=Ek i get 1.89 m/s as speed. What do i do now with it.
...

Ok, you used conservation of energy to get the corrrect initial velocity.

Now use the kinematic eqns to find out how far the eraser travels under a constant decelerating force of 0.042N with an initial velocity of 1.89m/s.