# Homework Help: Kinetic Energy

1. Oct 16, 2008

### Grogerian

1. The problem statement, all variables and given/known data
Find the total kinetic energy in the system. a explosion fires two pieces both 7.3m high and 11.2m horizontally total kinetic energy done by the explosion the first piece is 15kg, the second 26kg?

2. Relevant equations
kinematics
Ke=1/2(mv2)

3. The attempt at a solution
I found that Vi(y) = $$\sqrt{2(9.81)(-7.3)}$$ = 11.96 m/s do i just use this to find the total energy done? or do i need to consider the x-dir as well, If so how do i do that?

2. Oct 16, 2008

### tiny-tim

Hi Grogerian!

The KE depends on the total speed, as you know, so Vy is obviously not enough unless Vx is zero.

(but I can't help any furher, as I don't understand the question. )

3. Oct 16, 2008

### LowlyPion

Velocity is the sum of the components, so yes, you do need to determine the x component.

Since you can figure the time to drop 7.3m from the peak and you know that will be half the time of its flight, and you know that is 7.3m = 1/2 g*t2. Now you can figure how fast it was to go 11.3m.