1) Define what is meant by the half - radioactive material. 2) Radioactive decay is a random process. Explain what this means.
3) The activity of radioactive sample is measured. The activity corrected for background radiation is found to be 240 Bq. The activity is measured again after 1 hour 30 minutes and is now 30 Bq. What is the half life of the sample?

Acommercial refrigerator with refrigerant-134a as the working fluid is used to keep the refrigerated space at -35°c by rejecting waste heat to cooling water that enters the condenser at 18°c at a rate of 0.25 kg/s and leaves at 26°c. the refrigerant enters the condenser at 1.2 mpa and 50°c. if the compressor consumes 3.3 kw of power, determine (a) the mass flow rate of the refrigerant, (b) the refrigeration load, (c) the cop, and (d) the minimum power input to the compressor for the same refrigeration load.

Astudent pushes a 60-n block across the floor for a distance of 10 m. how much work was done to move the block

The gravitational force between pluto and charon is 3.61 × 1018 n. pluto has a mass of 1.3 × 1022 kg, which is only slightly greater than charon’s mass of 1.6 × 1021 kg. how far apart are pluto and charon? 2.0 × 107 m 2.4 × 1012 m 3.8 × 1014 m 5.8 × 1024 m