Velocity-time Graph

1 Study the velocity-time graph of motion of a car moving along a straight line and answer the following questions : 1. What is the displacement in 4 and 8 s ? 2. How far is the car from the starting point after 8 s ? 3. What is the average velocity of the car over 8 s ? 4. What is the distance moved by the car in 8 s ? 5. What is the average speed of the car over 8 s ? Author : S.C.Benjamin Note : Match your answers with the answers given on the next page. 2 Answers 1. The car moves along positive x-axis for first 4 seconds. Displacement is given by area between time axis and the v-t graph : 1 4 16 32 2 × × = m The car has negative velocity after 4 seconds. This means it is moving in negative x direction. Its displacement in the last 4 s is : 1 4 ( 8) 16 2 × × − = − m A displacement of –16 m in the last 4 s means it moves towards the point of start. Thus the net displacement in 8 s : + 32 m + ( -16 ) m = + 16 m 2. The car is 16 m away from the starting point. 3. The average velocity of the car is given by the net displacement divided by the time : 1 16 2 8 ms− = 4. The distance moved by the car over 8 s : 32 + 16 = 48 m. 5. The average speed of the car over 8 s is total distance divided by the total time 1 48 6 8 ms− = .