# Easy Kinetic Energy Problem

1. Sep 1, 2009

### kajasu88

1. The problem statement, all variables and given/known data
A cheetah whose weight is 419 N runs North at a speed of 112 km/h. What is the cheetah's kineticenergy? Is there a direction? Why or why not?

I got 2.68 x (10^5)
Is this wrong?

2. Sep 1, 2009

### Staff: Mentor

What units are you using? How did you calculate it? Show what you did.

3. Sep 1, 2009

### rock.freak667

That does not see correct. If it weighs 419N, what is its mass? Convert 112km/h into m/s

4. Sep 1, 2009

### kajasu88

i got the mass by dividing (419N)/(9.8m/s^2) because F=ma
then i plugged it into KE=(1/2)m(v^2)
V=112km/h (i left it in km/h b/c all the multiple choice answers were in km/h)

5. Sep 1, 2009

31.1m/s ??

6. Sep 1, 2009

### ideasrule

The answers were in km/h? But that's a unit of speed, not energy. Are you sure they weren't in joules (symbol J)?

7. Sep 2, 2009

### kajasu88

i figured it out!
so yes, 31.1 m/s
so KE=(1/2)m(v^2) .... (1/2)(419N / 9.8m/s^2)(31.1 m/s)^2
20,700 kg m^2/s^2

and i got the same answer as two other people