motion under gravity

Question

A ball is thrown vertically upward with a velocity of 20 m/s. What will be its velocity when it returns to the point of projection? (g = 10 m/s²)

RankGuru · Accepted Answer

1. **Symmetry of Motion**: For an object thrown upward under gravity (ignoring air friction), the time to rise equals the time to fall, and the speed at any level is the same during ascent and descent.
2. **Energy Logic**: By conservation of mechanical energy, the kinetic energy at the point of projection must be recovered when it returns to the same height.
3. **Calculation**:
   - Speed at return = Initial Speed = 20 m/s.
4. **Direction Aspect**: Initial velocity was upward ($+20$ m/s). Upon return, the ball is moving downward.
5. **Final Velocity**: $-20$ m/s (using sign convention where up is positive).

Rank Guru

motion under gravity

Select the correct option: