# Kinetic energy and work energy thereom

1. Sep 26, 2008

### amannaan2000

a 5.75 kg object is initially moving so that its x-component of velocity is 6.00m/s and its y-component is -2.00m/s. what is the kinetic energy of the object at this time. What is the change of kinetic energy do that its velocity is 8.50m/s in the x direction and 5.00m/s in the y direction

2. Sep 26, 2008

### Perillux

kinetic energy equals (1/2)m*v^2
You already know the mass and the 2 components of velocity, just use pythagorean theorem to find the actual velocity.

and since mass can't change, then change in kinetic energy is equal to (1/2)m*(change in velocity)^2

3. Sep 26, 2008

### St. Aegis

As perillux said, you use the pythagorean theorem to find the total velocity magnitude and use that and the given mass in the formula to get the answer.

4. Sep 27, 2008

### Staff: Mentor

Careful. This is incorrect.

$$\Delta {KE} = 1/2m\Delta(v^2) \ne 1/2m(\Delta v)^2$$