An ron ball with a diameter of d = 5 cm (λ = 60 w/mk, c.-460 j/kgk: rho = 7850 kg/m") originally had a temperature ta 225°c, suddenly the ball is streamed in by a cold fluid stream with a temperature of 25°c; the heat transfer coefficient is anid-500 w/mk. the following must be calculated: a) the temperature in the centre of the sphere 2 minutes after the start of cooling. b) the temperature inside the ball at a surface distance of 1 cm and after 2 min. c) what is the dissipated heat from the ball per m2 after this time?

What is avogadro’s number, and why is it useful

Long term exposure to waves can cause sunburns and skin cancer. a) visible b) infrared c) gamma rays d) ultraviole

Agroup of students is studying convection current. they fill two identical balloons with the same amount of helium. one balloon is placed in a freezer and the other is in an area with warm air. after 10 minutes, the balloon are released from a height of 1 meter. which of the following to the students most likely observe? a) the warm balloon expands and rises. the cold balloon shrinks and sinks b) the balloon both rise. the cold balloon is larger than the warm balloon c) the cold balloon expands and rises. the warm balloon shrinks and sinks d) the balloon rise at the same rate. both balloons are the same size