Problem 5P

A bottle has a mass of 35.00 g when empty and 98.44 g when filled with water. When filled with another fluid, the mass is 88.78 g. What is the specific gravity of this other fluid?

ANSWER: Your mass is 60 kg, Initial velocity u = 0.70 m/s, Final velocity v = 0.70 m/s Distance travelled through the moving sidewalk is 25 meters horizontally. a) The work-energy theorem tells us that, the work done on a system is the difference between initial and final kinetic energy. Mathematically, So, let’s calculate the difference in kinetic energy. The initial K.E was, 1/2 ×(60 kg×0.70 ) = 14.7 jules Final kinetic energy is, 2 1/2 ×(60 kg×0.70 ) = 14.7 jules So, K.E = 14.714.7 = 0. As there is no change in the kinetic energy, the work done is zero. b) The potential difference between the two levels will tell how much work has to be done, because this is the way we have defined gravitational potential energy. The gravitational potential energy at a certain distance “R” from the surface of earth is defined as, the amount of work we have to do to bring a mass from infinity to that distance “R”. So the difference between two potentials is the amount of work done to go from one potential to another. So, mathematically we have P.E P.E = work done final initial work done = mg (h h ) = 60 kg×9.8 m/s ×4.5 m = 2646 jules. 2 1 Therefore the escalator did 2646 jules of work on you. c) The down escalator does exactly same amount of work on you but with a minus sign. Because it’s moving in the direction of gravity. So the work done will be -2646 jules.