#### Answer

The sprinter's average power output is 1170 watts.
The greyhound's average power output is 2000 watts.

#### Work Step by Step

The work done by the sprinter is equal to the kinetic energy at 3.0 s. We can find the work $W_s$ done by the sprinter.
$W_s = KE$
$W_s = \frac{1}{2}mv^2$
$W_s = \frac{1}{2}(70~kg)(10~m/s)^2$
$W_s = 3500~J$
We can find the sprinter's average power output;
$P_{ave} = \frac{W_s}{t}$
$P_{ave} = \frac{3500~J}{3.0~s}$
$P_{ave} = 1170~watts$
The sprinter's average power output is 1170 watts.
The work done by the greyhound is equal to the kinetic energy at 3.0 s. We can find the work $W_{gh}$ done by the greyhound.
$W_{gh} = KE$
$W_{gh} = \frac{1}{2}mv^2$
$W_{gh} = \frac{1}{2}(30~kg)(20~m/s)^2$
$W_{gh} = 6000~J$
We can find the greyhound's average power output.
$P_{ave} = \frac{W_{gh}}{t}$
$P_{ave} = \frac{6000~J}{3.0~s}$
$P_{ave} = 2000~watts$
The greyhound's average power output is 2000 watts.