Solve the following half-life problems. 1. The half-life of Pa-234 is 6.75 hr. How much (what fraction) of a sample of this isotope remains
after 20.25 hr?

2. The half-life of Rn-222 is 3.823 day. What was the original mass of a sample of this isotope if
0.0500 g remains after 7.646 day?

3. The half-life of Th-227 is 18.2 day. How many days are required for 0.70g of a given sample to
decay to 0.0875 g?

4. The half-life of carbon-14 is 5700 years. If a 10 gram sample undergoes decay for 17,100 years,
how many half-lives have the sample undergone?

Athin plate moves between two parallel, horizontal, stationary flat surfaces at a constant velocity of v = 7.5 m/s. the two stationary surfaces are spaced 4 cm apart, and the medium between them is filled with oil whose viscosity is 0.9 n·s/m2. the part of the plate immersed in oil at any given time is 2 m long and 0.5 m wide. if the plate moves through the mid-plane between the surfaces, determine the force required to maintain this motion. what would your response be if the plate was 1 cm from the bottom surface (h2) and 3 cm from the top surface (h1)? if the plate moves through the mid-plane between the surfaces, the force required to maintain the motion will be n. if the plate was 1 cm from the bottom surface (h2) and 3 cm from the top (h1) surface, the force required to maintain the motion would be n.