91影视

Revisit Example 3鈥�7, and assume that the boy with the slingshot is below the boy in the tree (Fig. 3鈥�40) and so aims upward, directly at the boy in the tree. Show that again the boy in the tree makes the wrong move by letting go at the moment the water balloon is shot.

FIGURE 3-40Problem 36

A stunt driver wants to make his car jump over 8 cars parked side by side below a horizontal ramp (Fig. 3鈥�41). (a) With what minimum speed must he drive off the horizontal ramp? The vertical height of the ramp is 1.5 m above the cars and the horizontal distance he must clear is 22 m. (b) If the ramp is now tilted upward, so that 鈥渢akeoff angle鈥� is 7.0掳 above the horizontal, what is the new minimum speed?

FIGURE 3-41Problem 37

A person going for a morning jog on the deck of a cruise ship is running toward the bow (front) of the ship at 2.0 m/s while the ship is moving ahead at 8.5 m/s. What is the velocity of the jogger relative to the water? Later, the jogger is moving toward the stern (rear) of the ship. What is the jogger鈥檚 velocity relative to the water now?

Huck Finn walks at a speed of 0.70 m/s across his raft (that is, he walks perpendicular to the raft鈥檚 motion relative to the shore). The heavy raft is traveling down the Mississippi River at a speed of 1.50 m/s relative to the river bank (Fig. 3鈥�42). What is Huck鈥檚 velocity (speed and direction) relative to the river bank?

FIGURE 3-42Problem 39

Graphically determine the resultant of the following three vector displacements: (1) 24 m,${36}^o$north of east; (2) 18 m,${37}^o$east of north; and (3) 26 m,${33}^o$west of south.

A bullet fired from a rifle begins to fall

(a) as soon as it leaves the barrel

(b) after the air friction reduces its speed

(c) not at all if air resistance is ignored.

Can the displacement vector for a particle moving in two dimensions be longer than the length of the path traveled by the particle over the same time interval? Can it be less? Discuss.

Determine the speed of the boat with respect to the shore in Example 3鈥�10.

Two planes approach each other head-on. Each has a speed of 780 km/h, and they spot each other when they are initially 10.0 km apart. In how much time do the pilots have to take evasive action?

A passenger on a boat moving at 1.70 m/s on a still lake walks up a flight of stairs at a speed of 0.60 m/s (Fig. 3鈥�43). The stairs are angled at 45掳, pointing in the direction of motion as shown. What is the velocity of the passenger relative to the water?

FIGURE 3-43 Problem 42