2.4.1 A First Look at Projectile Motion Flashcards
A First Look at Projectile Motion
- The vector forms of the master equations of kinematics for constant acceleration can be used to describe free fall in two dimensions.
- To solve a projectile motion problem you need to know the initial position and velocity of the object.
- Two objects simultaneously dropped to the ground will land at the same instant, even if one has horizontal velocity
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- Projectile motion is free fall in two dimensions. Examples of objects experiencing projectile motion are a rocket after its engines stop, a high jumper making a jump, a baseball thrown through the air and the dart shot out of a toy gun. You already know that objects in free fall accelerate downward at .The master equations of kinematics with constant acceleration can be used to describe projectile motion.
- Because objects in free fall accelerate only in the vertical direction, the horizontal component of acceleration is zero.The terms containing ax drop out of the x-components of projectile motion. An important consequence is that the horizontal velocity is constant in projectile motion.
- The value of ay in the y-component forms of the equations of kinematics is when the coordinate system points in the downward direction and when the coordinate system points in the upward direction.
- Two balls are ejected simultaneously from a platform above the ground. One ball falls directly to the ground. The other ball has an initial velocity in the x-direction. The balls land at the same instant. Motion in the x-direction is independent from motion in the y-direction. Because both balls have identical initial position, velocity and constant acceleration in the y-direction, their vertical paths are identical. The horizontal component of both balls’ velocity remains constant throughout the fall: in one case it is zero in the other case it is vix.
- Thelma and Louise drive their car off a 500 m cliff at .You can calculate how long it takes them to reach the ground using the y-components of the second equation of kinematics.Choose a coordinate system where the ground is at 0 m and up is in the positive direction. The value of yi is 500 m,and . You can solve for Dt to find that it takes about 10 s for the car to land.
How long will it take for a ball, with initial horizontal velocity of 80 m / s, to hit the ground from a height of 400 m? Also, what is the range of the ball?
t = 9.0 s; range = 720 m
Which of the following statements about projectile motion is not correct?
In projectile motion, the motion can be broken down into perpendicular components that are interdependent.
Which of the following motion events is not an example of projectile motion?
a hockey puck sliding across an ice rink
Which of the following statements related to the y-component of projectile motion is not correct?
The acceleration, ay, is constant (and is always-9.8 m / s2 ).
Which of the following statements best describes the x-component of projectile motion?
The velocity is constant and the acceleration is zero.
How long will it take for a ball, with an initial horizontal velocity of 96 m / s, to hit the ground from a height of 800 m? Also, what is the range of the ball?
t = 12.8 s; range = 1,229 m
How long will it take for a ball to hit the ground if it is dropped from a height of 50 m?
3.2 s
Two identical balls are dropped at the same time. One ball drops straight down, while the other ball is given a horizontal push. Which of the following statements is not correct?
The horizontal motions of the two balls differ only by their xf values.
An object undergoes projectile motion. You are given the initial velocity of the object in the x-direction, vi x. Assuming the object has not yet collided with the ground, which of the following best describes how you would calculate the final velocity of the object, vf x, after a specific time, t ?
Because you already know that ax = 0, you can assume that vfk = vix
