A 0.14kg pinecone falls 16m to the ground, where it lands with a speed of 13m/s. With what speed would the pinecone have landed if there had been no air resistance?

The potential energy of the pinecone before it drops is mgh (given the ground is used as the zero potential energy reference). After if falls the energy is all kinetic energy or (1/2)mv^2 Equating these gives v^2 = 2gh. Note that you can now determine the energy loss due to air friction by the difference in kinetic energy of the two cases. You will need the mass for this calculation.