A 5 kg object falls from rest through 20 m and reaches speed 10 m/s. Work by air resistance is −250n J. Find n (take g=10 m/s²).
Physics · Mixed Chapter
JEE Main Practice

Question

A 5 kg object falls from rest through 20 m and reaches speed 10 m/s. Work by air resistance is −250n J. Find n (take g=10 m/s²).

G1 Physics · Accepted Answer

Step 1: Gravitational work Wg=mgh=5×10×20=1000 J. Step 2: Final kinetic energy ΔK=½mv²=½×5×10²=250 J. Step 3: Work–energy theorem: Wg+Wair=ΔK⇒Wair=250−1000=−750 J. Step 4: −250n=−750⇒n=3.