http://www.nikonchat.com/auto-nikkor-lens/

Is the Nikkor 50 mm f/1.8D AF Nikon D3100?
I keep getting mixed responses .. Perhaps this question will fhotoace
Short Answer: No, the 50mm f/1.8D lens is a AF lens, so the camera needs an autofocus motor, something that the D3100 does not for autofocus, you must obtain 50mm f/1.8G Lens is an AF-S, autofocus without AF the engine in the camera. http://www.bhphotovideo.com/c/product/766516-USA/Nikon_2199_AF_S_Nikkor_50mm_f_1_8G.html
nikon 70-300mm f/4.5-5.6G ED IF AF-S VR Nikkor Zoom Lens for nikon digital slr Cameras