In a solar water heater, energy from the sun is gathered by water that circulates through tubes in a rooftop collector. The solar radiation enters the collector through a transparent cover and warms the water in the tubes; this water is pumped into a holding tank. Assume that the overall efficiency of the system is 20% (that is, 80% of the incident solar energy is lost from the system). What collector area is necessary to raise the temperature of 400 L (L = liters) of water in the tank from 20 C to 40 C in 1.0 hr when the intensity of incident sun light is 750 W/m^2? You need to know that the density of water is 1 kg/L. 

iron would move it is magnetic there is a mag field around the current in the wire

current flows in a wire

note: the given question is incomplete.

complete question is given below.

which is an example of kinetic energy?

a. the energy stored in ethanol  

b. a hockey puck sliding across the ice  

c. a compressed spring  

d. a ball sitting at the top of a ramp

solution: the kinetic energy is the energy posses by the virtue of the motion of the object.

in the given options, a, c and d are the example of potential energy because it is the energy posses by the virtue of the rest of the object. but option b has the kinetic energy as the object is in motion.

hence, a hockey puck sliding across the ice   is the apex example of kinetic energy.

so, the option (b) a hockey puck sliding across the ice   is the correct option.