NEETPhysicsMotion in One Dimension
A car travelling on a straight highway covers one-third of its total journey distance at a speed of 10 km/h , and the remaining two-thirds of the distance at a speed of 60 km/h . The average speed of the car for the entire journey is
Options
- A22.5 km/h
- B35 km/h
- C120 7 km/h
- D130 3 km/h
Correct answer
A. 22.5 km/h
Step-by-step solution
Let the total distance of the journey be 3x . The distance covered in the first part is x at a speed of v₁ = 10 km/h . Time taken for the first part, t₁ = x 10 h . The distance covered in the second part is 2x at a speed of v₂ = 60 km/h . Time taken for the second part, t₂ = 2x 60 = x 30 h . Total time taken, T = t₁ + t₂ = x 10 + x 30 = 3x + x 30 = 4x 30 = 2x 15 h . Average speed is defined as the ratio of total distance to total time: v_ avg = Total distance Total time = 3x 2x 15 = 45 2 = 22.5 km/h . Answer: 22.5