question_answer

Speed-time graph of a car is shown in the figure given below. (a) How far does the car travel in the first 4 seconds? Shade the area on the graph. (b) What does the straight part of the graph represent?

Answer:

(a) Distance travelled by the car in first 4 seconds \[=Average\,\,speed\times Time\] The speed at 4th second is \[650\,m{{s}^{-1}}.\]So, Average speed of the car \[=\frac{0+650}{2}=\frac{650}{2}=325\,m{{s}^{-1}}\] So, Distance travelled by the car \[=325m{{s}^{-1}}\times 4s=1300m\] (b) The limiting flat portion of the curve describes the constant speed of the car, i.e., a speed of \[700\,m{{s}^{-1}}.\] At this stage, the acceleration of the car is zero.