A student throws a set of keys vertically upward to her sorority sister, who is in a window 4 m above. The keys are caught 1.5 s later by the sister's outstretched hand. (a) With what initial velocity were the keys thrown? (b) What was the velocity of the keys just before they were caught?

14. A train moving at an average speed of \( 72 \mathrm{~km} / \mathrm{h} \) takes 15 seconds to completely cross a bridge that is 80 metres long (a) Express \( 72 \mathrm{~km} / \mathrm{h} \) in metres per second (b) Find the length of the train in metres ( 2 mk )

Problem (2) \( A \) iniform ladder \( A B \) of weight 10 kg .w and 3 m length rests with its end \( A \) on a smooth horizomal noor and is end B on a smooth vertical wall. the ladder is kept in equilibritum by a rope tied to on of irs ends A. and irs other end is attached to a point on the hori=ontal plane vertically below B. if the ladder is inclined at \( +5^{\circ} \) to the horizontal, a man of weight 60 kg . w was ascending the ladder find the magnitude of the tension in the rope when the man is \( 2 m \) away from \( A \) \( \qquad \) \( \qquad \)

La cantidad de un material radiactivo disminuye a la mitad cada 10 años. Si comenzamos con 80 gramos, ¿cuánto quedará después de 30 años?

A 1 km long goods train is running at a speed of 45 \( \mathrm{~km} / \mathrm{h} \). The time taken by this goods train to pass through a 2 km long tunnel is: \( \begin{array}{ll}\text { (A) } 1 \text { minute } & \text { (B) } 2 \text { minutes } \\ \text { (C) } 3 \text { minutes } & \text { (D) } 4 \text { minutes }\end{array} \)

Sebuah mobil bermassa 1200 kg bergerak dengan kecepatan \( 20 \mathrm{~m} / \mathrm{s} \). Mobil tersebut kemudian direm hingga berhenti setelah menempuh jarak 50 meter. Berapakah gaya pengereman yang bekerja pada mobil tersebut?