Practice question

Given: A man runs at 5 m/s towards a wall and throws a ball at 15 m/s towards the wall when 20 m away. If the ball rebounds at 10 m/s, when does it return to the man? (Take wall as origin) These values define the system as per NCERT data. Formula: Relative speed towards wall = 15 + 5 = 20 m/s. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Time to hit wall: t_1 = 20/20 = 1 s . Man’s position = 5 · 1 = 5 m from wall. Ball rebounds at 10 m/s, relative speed = 10 - 5 = 5 m/s towards man. Time to return: t_2 = 5/5 = 1 s . Total time = 1 + 1 = 2 s . Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.