Question: how to install qwt in qt 5?
Answer: cd qwt-6.1.5. /usr/local/Qt-5.0.1/bin/qmake qwt.pro. ... 
make. ( On multicore systems you can speed up building the Qwt libraries with running several jobs simultaneously: f.e. "make -j4" on a dual core. ) ... 
sudo make install. ... 
cd qwt-6.1.5. ... 
mingw32-make. ... 
mingw32-make install. ... 
nmake. ... 
nmake install.