Work-Energy Theorem

[MDJerome]

I'm confused about why I'm not getting the same answer using two different methods (according to Work-Energy Theorem).

Here's the question:

An object of mass 10kg moves with a velocity of 4 m/s to the north. What is its kinetic energy?

I understand I can use the equation 1/2mv^2 = KE (equals 80 N)

But why can't I use Force x Velocity = KE

The force applied would have to equal 100 N to balance the weight of Gravity right?

So then, 100 N x 4m/s = 400 N.

This answer is different 80 N answer using the KE equation. Can someone explain to me why this doesn't work please or what I'm not understanding? Thanks.

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[GRod18]

No, if velocity is constant that means you don't have a net force.

because you don't have acceleration so F = ma = 0 net force.

 

[MDJerome]

Lol, sorry ignore that. I'm confusing my equation for Power. Embarrasing.

 

[MDJerome]

No, if velocity is constant that means you don't have a net force.

because you don't have acceleration so F = ma = 0 net force.

Silly mistake I made! Thanks haha

 

[lorenzomicron]

1/2mv^2 = 80 Joules (N is for force)


I'm not sure where weight is coming in here; the object is moving North not falling (I'm assuming as that is not northwards).