question_answer 10)

A player throws a ball upwards with an initial speed of . (i) What is the direction of acceleration during the upward motion of the ball ? (ii) What are the velocity and acceleration of the ball at the highest point of its motion ? (iii) Choose the x = 0 and t = 0 to be the location and time of the ball at its highest point, vertically downward direction to be the positive direction of X-axis, and give the signs of position, velocity and acceleration of the ball during its upward, and downward motion. (iv) To what height does the ball rise and after how long does the ball return to the player's hands ? (Take  and neglect air resistance).  

Answer:

(i) The ball moves under the effect of gravity. The direction of acceleration due to gravity is always vertically downwards. (ii) At the highest point, velocity of the ball = 0. Acceleration = Acceleration due to gravity 'g'                  (vertically downwards) (iii) When the highest point is chosen as the location for x = 0 and t = 0 and vertically downward direction to be the positive direction of X-axis: During upward motion. Position is positive, velocity is negative and acceleration is positive. During downward motion. Position is positive, velocity is positive and acceleration is positive. (iv) For upward motion.   If s is the height to which the ball rises, then                 or            or              Negative sign shows that the distance is covered in upward direction. If the ball reaches the highest point in time i, then   or           or              As    time of ascent = time of descent             Total time taken = 3 + 3 = 6 s.