Question

How fast should a man of 50kg runs so that his kinetic energy be 625joules

Answer 1

$1 \div 2 \: mv {}^{2} = 625 \\ mv { }^{2} = 1250 \\ 50 \times v {}^{2} = 1250 \\ v {}^{2} = 25 \\ v = 5$
the man will run with the velocity of 5m/s

Answer 2

k.E.=1/2×mv^2

625=1/2×50×v^2
625=25×v^2
v^2=25
v=√25
v=5m/s