Hello Aspirant,

Since mechanics and  mathematical physics are the core subjects in semester 1 , below are the some best books prescribed by DU :

For Mechanics:

An introduction to mechanics, D. Kleppner, R.J. Kolenkow, 1973, McGraw-Hill.

Mechanics, Berkeley Physics, vol.1, C. Kittel, W. Knight,2007, Tata McGraw-Hill.

Physics, Resnick, Halliday and Walker 8/e. 2008, Wiley.

Analytical Mechanics, G.R. Fowles and G.L. Cassiday. 2005, Cengage Learning.

Feynman Lectures, Vol.I, R.P.Feynman, R.B.Leighton, M.Sands, 2008, Pearson

Education

Mechanics, D.S. Mathur, S.Chand and Company Limited, 2000

University Physics. F.W Sears, M.W Zemansky, H.D Young 13/e, 1986, Addison Wesley

Physics for scientists and Engineers with Modern Phys., J.W.Jewett, R.A.Serway, 2010,Cengage Learning

Theoretical Mechanics, M.R. Spiegel, 2006, Tata McGraw Hill.

For Mathematical physics:

Mathematical Methods for Physicists, G.B.Arfken, H.J.Weber, F.E.Harris,2013, 7th Edn., Elsevier.

An introduction to ordinary differential equations, E.A. Coddington, 2009, PHI learning

Differential Equations, George F. Simmons, 2007, McGraw Hill.

Advanced Engineering Mathematics, D.G. Zill and W.S.Wright, 5 Ed., 2012, Jones and Bartlett Learning

Mathematical Physics, Goswami, 1st edition, Cengage Learning

Engineering Mathematics, S.Pal and S.C. Bhunia, 2015, Oxford University Press

Advanced Engineering Mathematics, Erwin Kreyszig, 2008, Wiley India.

Vector Analysis, M.R. Spiegel, McGraw-Hill

Introduction to Electrodynamics, David J. Griffiths, Pearson

You may find all these books as well as other useful reference books  in your college library.

All the best