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A rescue plane wants to drop supplies to isolated mountain climbers on a rocky ridge 235 m below. If the plane is traveling horizontally with a speed of 250 km/h (69.4 m/s), how far in advance of the recipients (horizontal distance) must the goods be dropped (Fig. 3鈥38)?

FIGURE 3-38Problem 31

Short Answer

Expert verified

The goods must be dropped 480.94 m before the recipients so that the goods can reach them.

Step by step solution

01

Step 1. Kinematics equation for projectile motion

When a projectile is projected horizontally from a height yabove the ground with initial velocity vx0, it moves under the effect of two independent velocities vxand vy. If the starting point is taken as the origin, and the downward direction is taken as the positive y-axis, the horizontal and vertical components of acceleration will be ax=0;ay=g. Thus, the kinematics equations for the projectile motion are as follows:

  • The kinematics equations for the horizontal motion of projectile are as follows:

vx=vx0x=vx0t

  • The kinematic equationsfor the vertical motion of projectile are as follows:

vy=vy0+gty=vy0t+12gt2vy2=vy02+2gy

Here, xandy are the horizontal and vertical displacements of the projectile traveled in time t.

02

Step 2. Given information

The vertical displacement of the projectile is y=235m.

The initial horizontal velocity of the projectile is vx0=69.4m/s.

The initial vertical velocity of the projectile is vy0=0m/s.

Here, the goods thrown by the plane is your projectile. Let the horizontal displacement of the projectile bex and the time taken by the projectile to reach the ground be t.

03

Step 3. Determination of the time taken by the goods to reach the ground

Using the kinematics equation for the vertical motion of a projectile, you will get the time as

y=vy0t+12gt2235m=0m/st+129.8m/s2t2t2=2235m9.8m/s2t2=47.96s2t=6.93s

04

Step 4. (b) Determination of the time needed by another car to reach the speed limit

Using the kinematics equation for the horizontal motion of a projectile, you will get the horizontal distance as

x=vx0t=69.4m/s6.93s=480.94m.

Thus, the horizontal distance traveled by the goods is 480.94 m.

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Most popular questions from this chapter

A projectile is shot from the edge of a cliff 115 m above ground level with an initial speed of 65.0 m/s at an angle of35.0with the horizontal plane, as shown in Fig, 3-51. (a) Determine the time taken by the projectile to hit point P at ground level. (b) Determine the distance X of point P from the base of the vertical cliff. At the instant just before the projectile hits point P, find (c) the horizontal and the vertical components of its velocity, (d) the magnitude of the velocity, and (e) the angle made by the velocity vector with the horizontal. (f) Find the maximum height above the cliff top reached by the projectile.

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