To see if this acceleration can be reached by the actual system, the engineers in the video conduct an experiment using a scale model of the glider system. in the scale model, they launch a piece of wood covered in fabric from a height of about 30 feet, using a bathtub full of water as the counterweight the result of this test shows that they did not reach the acceleration they had hoped for. now the engineers are faced with a problem: they must find a new way to launch the glider so that they can reach the desired speed and accelera- tion. they are forced to revise both the parameters of the experiment and their mathematical models. questions 3. is it possible for the bathtub to accelerate at 1.2g? explain why or why not. if it is not possible, how could you modify the system to generate this acceleration? 4. why would they use a scaled-down model to test their ideas? what are the benefits of this approach? what are the limitations of this model?

Aheat engine running backward is called a refrigerator if its purpose is to extract heat from a cold reservoir. the same engine running backward is called a heat pump if its purpose is to exhaust warm air into the hot reservoir. heat pumps are widely used for home heating. you can think of a heat pump as a refrigerator that is cooling the already cold outdoors and, with its exhaust heat qh, warming the indoors. perhaps this seems a little silly, but consider the following. electricity can be directly used to heat a home by passing an electric current through a heating coil. this is a direct, 100% conversion of work to heat. that is, 19.0 \rm kw of electric power (generated by doing work at the rate 19.0 kj/s at the power plant) produces heat energy inside the home at a rate of 19.0 kj/s. suppose that the neighbor's home has a heat pump with a coefficient of performance of 4.00, a realistic value. note: with a refrigerator, "what you get" is heat removed. but with a heat pump, "what you get" is heat delivered. so the coefficient of performance of a heat pump is k=qh/win. an average price for electricity is about 40 mj per dollar. a furnace or heat pump will run typically 200 hours per month during the winter. what does one month's heating cost in the home with a 16.0 kw electric heater? what does one month's heating cost in the home of a neighbor who uses a heat pump to provide the same amount of heating?