21. Blood flows at an average speed of \( 0.40 \mathrm{~m} / \mathrm{s} \) in a horizontal artery of radius 1.0 cm . The average pressure is \( 1.4 \times 10^{4} \mathrm{~N} / \mathrm{m}^{2} \) above atmospheric pressure (the gauge pressure). (a) What is the average speed of the blood past a constriction where the radius of the opening is 0.30 cm ? (b) What is the gauge pressure of the blood as it moves past the constriction?

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

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 \( A \) \( \qquad \) \( \qquad \)

An object of mass 0.1 kg , which is fastened at one end of a cord of length L , is whirled about a vertical circle. The tangential speed of the object when the cord makes \( 53^{\circ} \) with the vertical and moving down is \( 5 \mathrm{~m} / \mathrm{s} \) and the tension in the cord at this time is \( \mathrm{T}_{1}=\mathrm{T} \). When the angle is reduced to \( 37^{\circ} \), the speed becomes \( 8 \mathrm{~m} / \mathrm{s} \) and the tension through the cord doubles. Find the length \( L \) and the tension T .

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: \( \begin{array}{ll}\text { (A) } 1 \text { minute } & \text { (B) } 2 \text { minutes } \\ \text { (C) } 3 \text { minutes } & \text { (D) } 4 \text { minutes }\end{array} \)

A boat is supposed to travel with a velocity vector of \( \langle 40,30\rangle \), but the current has a velocity vector of \( \langle 0,-5\rangle \). What is the boat's actual velocity vector? \( \langle 45,30\rangle \) \( \langle 40,25\rangle \) \( \langle 40,35\rangle \)