Physics for the BUET Written Paper
What the paper rewards
BUET physics questions test whether you can reason from a small set of laws rather than recall formulas in isolation. Build fluency in Newtonian mechanics (projectile motion, circular motion, work-energy, collisions), rotational dynamics (torque, moment of inertia, angular momentum), oscillations and waves, geometrical and wave optics, electrostatics and circuits, and basic modern physics. Be equally comfortable with SI units, dimensional analysis, and graph interpretation.
Concepts you must own
Know when energy conservation is safer than force analysis, when momentum is conserved, and the conditions under which mechanical energy is not. For SHM, connect displacement, velocity, and acceleration through phase. For optics, distinguish real and virtual images and track sign conventions. For circuits, apply Kirchhoff's rules systematically rather than guessing.
Traps that cost marks
- Mixing up angular velocity and linear velocity in rolling problems.
- Forgetting that tension does work in pulley systems even though it is internal to the whole system.
- Assuming maximum range always occurs at 45 degrees when launch and landing heights differ.
- Using the wrong refractive index when light passes through multiple media.
- Ignoring internal resistance when computing terminal voltage.
Worked rule of thumb
A ball is thrown horizontally at 15 m/s from a 20 m cliff. Time to fall: t = sqrt(2h/g) = sqrt(40/9.8) ≈ 2.02 s. Horizontal range: x = 15 × 2.02 ≈ 30.3 m. The key idea: horizontal and vertical motions are independent, so the horizontal speed does not affect fall time. Whenever a problem separates into independent components, solve each component alone and then recombine.
Exam strategy
Draw the free-body diagram first, name knowns and unknowns, choose the conservation law that avoids unnecessary intermediate variables, and check units and limiting cases at the end.