The half-life of plutonium-238 is 87.7 years. what percentage of the atoms in a sample of plutonium-238 will remain radioactive after 263.1 years?

According to social exchange theory, altruistic behaviors benefit the individual who performs them. t/f

True or false: the revolution of the earth creates day and night as it rotates around the sun

Aperson stands on a platform, initially at rest, that can rotate freely without friction. the moment of inertia of the person plus the platform is ip. the person holds a spinning bicycle wheel with its axis horizontal. the wheel has moment of inertia iw and angular velocity ωw. take the ωw direction counterclockwise when viewed from above. part a what will be the angular velocity ωp of the platform if the person moves the axis of the wheel so that it points vertically upward?