Water and then oil (which don’t mix) are poured into a U-shaped tube, open at both ends. They come to equilibrium as shown in Fig. 10–49. What is the density of the oil? [Hint: Pressures at points a and b are equal. Why?]

ANSWER:STEP 1:-The speed of the fastest human is 11 m/s.Let’s say, his mass is “m”.The kinetic energy will be, K.E = 1/2 m V = 1/2 × m × 11 = 1/2 × m × 121 = 60.5 m jules.The potential energy or the gravitational potential energy he would have at a height “h”, P.E = mgh--------------(1)According to our requirement, both the energies should be the same. So, the height at whichthe condition would satisfy is, K.E = P.E 60.5 m = mgh = m × 9.8 × h h = 60.5 m / 9.8 m h = 6.172 meters.CONCLUSION:So, at a height of 6.172 meters the sprinter will attain the potential energy equal to the kineticenergy of world’s fastest man running at the speed of 11 m/s.