19. The resistance R to the motion of a car is partly constant and party proportional to the square of the speed V . When the speed is \( 30 \mathrm{~km} / \mathrm{hr} \), the resistance is 190 N and when the speed is \( 50 \mathrm{~km} / \mathrm{hr} \), the resistance is 350 N . Find for what speed the resistance is 302.5 ohms. (WAEC)

हल दिया है-गेंद का प्रारम्भिक वेग \( 20 \mathrm{~cm} \mathrm{~s}^{-1} \) है। मेज के द्वारा गेंद पर घर्षण बल लगने के कारण गेंद का वेग 10 s में शून्य हो जाता है। वेग-समय ग्राफ एक सरल रेखा है जिससे यह पता चलता है कि गेंद एक नियत त्वरित बल के साथ चलती है।

Una palla di massa \( m_{1}=24 \mathrm{~g} \), che viaggia alla velocità \( v_{1} \), urta elasticamente una palla ferma di massa \( m_{2}=\frac{1}{2} m_{1} \). Dopo l'urto, la seconda palla va a colpire elasticamente una terza palla ferma, di massa \( m_{3} \). Tutti gli urti avven- gono lungo la stessa retta. Quale deve essere la massa \( m_{3} \) affinché la sua velocita dopo l'urto sia uguale a \( v_{1} \) ?

Quelle est l'unité de la valeur d'une tension? Quelle est l'unité de la valeur d'une intensité ?

(a) 8 (b) \( 8 \sqrt{2} \quad(c) 8 \sqrt{3} \quad(d) 12 \) (49) A uniform rod \( \overline{A B} \) of length 6 meters and weight \( 8 \mathrm{~kg} \cdot \mathrm{wt} \). is attached to a hinge fixed in a vertical wall at its end A the rod is kept horizontal by attaching it at a point C on the rod (where \( A C=4 \) meters) by a string which its other end is fixed at the point D on the wall above A exactly and at a distance 4 meters from it. Calculate the magnitude of the tension in the string and the reaction of the hinge.

Train moving with speed of \( (40 \mathrm{~m} / \mathrm{s}) \) the driver have resorted to the use of brakes to reduce the speed of the train movement by rate \( \left(-2 \mathrm{~m} / \mathrm{s}^{2}\right) \) Calculate: a) The amount of time it takes for the train even stops completely. b) The amount of distance traveled since the train began braking until it stops