3 A 210 W heater is placed in 2 kg of water and switched on for 200 seconds.
a How much energy is needed to raise the
temperature of 2 kg of water by 1 °C?
b How much energy does the heater supply?
C Assuming that no thermal energy is lost, what is the
temperature rise of the water?

Large electric fields in cell membranes cause ions to move through the cell wall. the field strength in a typical membrane is 1.0 x 10 7 n/c. what is the magnitude of the force on a calcium ion with charge +e? what is its acceleration? is it possible for a particle with the same charge as as calcium to have a different acceleration if placed at this location? what would change the acceleration: mass of the particle? diameter of the particle?