What is albert einstein’s contribution to the understanding of nuclear energy?

he proposed that matter can be converted to energy and vice versa.
he first discovered that nuclear-reaction products are lighter than the reactants.
he developed the use of nuclear reactions to generate electricity.
he demonstrated that a uranium nucleus splits and releases neutrons.

Given the position vector of the particle r(t)=(t+1)i+(t^2−1)j+2t k, find the particle's velocity and acceleration vectors at t=1

The ratio of lift to drag l/d for a wing or airfoil is an important aerodynamic parameter, indeed, it is a direct measure of the aerodynamic efficiency of the wing. if a wing is pitched through a range of angle of attack, l/d first increases, then goes through a maximum, and then decreases. consider an infinite wing with an naca 2412 airfoil. estimate the maximum value of l/d. assume that the reynolds number is 9x10^6.

Is a volume of space that is empty of matter.