Class work 1. A girl thows a ball upwards, moving it an initial speed u=15m/s Neglect air resistance a) How long does the ball take to return to the girl's hand? b) What will be its velocity then? 2. A ball is thrown upward. While the ball is in free fall, does its acceleration (a)increase (b) decrease (c) increase and then decrease (d) decrease and then increase (e)remain constant? 3. After a ball is thrown upward and is in the air, its speed (a)increases (b)decreases (c) increases and then decreases (d) decreases and then increases (e) remains the same.

1. <br />a) The time taken for the ball to return to the girl's hand can be calculated using the formula: <br />\[ t = \frac{2u}{g} \]<br />where \( u \) is the initial speed and \( g \) is the acceleration due to gravity. <br />\[ t = \frac{2 \times 15}{9.8} \approx 3.06 \, \text{seconds} \]<br /><br />b) The velocity of the ball when it returns to the girl's hand will be equal in magnitude but opposite in direction to the initial velocity. Therefore, the velocity will be \(-15 \, \text{m/s}\).<br /><br />2. The acceleration of the ball during free fall remains constant. The correct answer is (e) remain constant.<br /><br />3. After a ball is thrown upward, its speed (b) decreases until it reaches the maximum height, after which it (c) increases and then decreases as it falls back to the ground.