Give me a stock clerk with a goal, and I will give you a man who will make history. Give me a man without a goal, and I will give you a stock clerk. – **J.C. Penny**

# Lecture 9 Motion in a straight line

**Exercise 3.4** A drunkard walking in a narrow lane takes 5 steps forward and 3 steps backward, followed again by 5 steps forward and 3 steps backward, and so on. Each step is 1 m long and requires 1 s. Plot the x-t graph of his motion. Determine graphically and otherwise how long the drunkard takes to fall in a pit 13 m away from the start.

**Exercise 3.5** A jet airplane travelling at the speed of 500 km h^{–1} ejects its products of combustion at the speed of 1500 km h^{–1} relative to the jet plane. What is the speed of the latter with respect to an observer on the ground ?

**Exercise 3.6** A car moving along a straight highway with speed of 126 km h^{–1} is brought to a stop within a distance of 200 m. What is the retardation of the car (assumed uniform), and how long does it take for the car to stop ?

**Exercise 3.7** Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of 72 km h^{–1} in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1 m s^{–2}. If after 50 s, the guard of B just brushes past the driver of A, what was the original distance between them ?