In: Physics
You launch a projectile horizontally from a building 29.5 m above the ground at another building 40.6 m away from the first building. The projectile strikes the second building 14.0 m above the ground. What was the projectile s launch speed?
22.84 m/s |
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16.56 m/s |
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24.03 m/s |
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30.04 m/s |
As the projectile is launched horizontally, the initial vertical velocity of the projectile is zero uy=0. Initial height of the projectile is ho=29.5m. We want to find the time in which the height of the projectile becomes h=14.0m. We know that the vertical acceleration of a projectile near the surface of the Earth is ay=-9.8m/s2. The vertical acceleration is constant, the vertical motion is governed by the kinematics equation for uniformly accelerated motion. To find the time we use
Substituting values
The horizontal acceleration is zero, the horizontal velocity does not change with time. The projectile covered horizontal distance 40.6m (which is the horizontal distance between the two buildings) in 1.779 seconds. The horizontal velocity is
Since the projectile was thrown horizontally and the horizontal velocity does not change with time, the launch speed of the projectile is 22.82m/s. The first option is correct.