魅影直播

When Babe Ruth hit a homer over the 8.0-m-high right field fence 98 m from home plate, roughly what was the minimum speed of the ball when it left the bat? Assume the ball was hit 1.0 m above the ground and its path initially made a 36掳 angle with the ground.

At serve, a tennis player aims to hit the ball horizontally. What minimum speed is required for the ball to clear the 0.90-m-high net about 15.0 m from the server if the ball is 鈥渓aunched鈥� from a height of 2.50 m? Where will the ball land if it just clears the net (and will it be 鈥済ood鈥� in the sense that it lands within 7.0 m of the net)? How long will it be in the air? See Fig. 3鈥�54.

Spymaster Chris, flying a constant 208 km/h horizontally in a low-flying helicopter, wants to drop secret documents into her contact鈥檚 open car which is traveling 156 km/h on a level highway 78.0 m below. At what angle (with the horizontal) should the car be in her sights when the packet is released (Fig. 3鈥�55)?

A basketball leaves a player鈥檚 hands at a height of 2.10 m above the floor. The basket is 3.05 m above the floor. The player likes to shoot the ball at a 38.0掳 angle. If the shot is made from a horizontal distance of 11.00 m and must be accurate to$\mathbf{卤}\mathbf{0}\mathbf{.}\mathbf{22}\mathbf{m}$(horizontally), what is the range of initial speeds allowed to make the basket?

A boat can travel$2.20\mathrm{m}/\mathrm{s}$in still water. (a) If the boat points directly across a stream whose current is$1.20\mathrm{m}\mathbf{/}\mathbf{s}$, what is the velocity (magnitude and direction) of the boat relative to the shore? (b) What will be the position of the boat, relative to its point of origin, after 3.00 s?

Two vectors have length$V_1=3.5\mathrm{km}$and$V_2=4.0\mathrm{km}$. What are maximum and minimum magnitude of their vector sum?

You are riding in an enclosed train car moving at 90 km/h. Where will the baseball land if you throw it straight upward?

(a) In front of you

(b) Behind you

(c) On your hand

(d) Can鈥檛 be decided from the given information

Figure 3-33 shows two vectors,$\stackrel{鈫�}{A}$and$\stackrel{鈫�}{B}$, Whose magnitudes are A = 6.8 units and B = 5.5 units. Determine$\stackrel{鈫�}{C}$if (a)$\stackrel{鈫�}{C}=\stackrel{鈫�}{A}+\stackrel{鈫�}{B}$(b)$\stackrel{鈫�}{C}=\stackrel{鈫�}{A}-\stackrel{鈫�}{B}$(c)$\stackrel{鈫�}{C}=\stackrel{鈫�}{B}-\stackrel{鈫�}{A}$. Give the magnitude and direction for each.

Figure 3-33 Problem 7

A Projectile is launched from ground level to the top of a cliff which is 195 m away and 135 m high (see Fig. 3-56). If the projectile lands on top of the cliff 6.6 s after it is fired, find the initial velocity of the projectile (magnitude and direction). Neglect air resistance.

FIGURE 3-56Problem 70

A basketball is shot from an initial height of 2.40 m (Fig. 3-57) with an initial speed$v_0=12\mathrm{m}/\mathrm{s}$directed at an angle${胃}_0={35}^o$above the horizontal. (a) How far from the basket was the player if he made a basket? (b) At what angle to the horizontal did the ball enter the basket?

FIGURE 3-57Problem 71