Question

3) A soccer ball is kicked with an initial horizontal speed of 8 m/s and an initial vertical speed of 6

m/s. Identify the following quantities and include one short sentence to explain your answer using

the concepts of projectile motion (no calculations are necessary). Assume that projection and

landing height are the same and neglecting air resistance (4 pts):

a) The ball’s horizontal speed 0.5 seconds into its flight is:

because:

b) The ball’s horizontal speed midway through its flight is:

because:

c) The ball’s horizontal speed immediately before contact with the ground is:

because:

d) The ball’s vertical displacement up is (circle one) greater than/less than/the same as the

vertical displacement down because:

e) The ball’s vertical velocity halfway through its flight is:

because:

f) The ball’s vertical speed immediately before contact with the ground is:

because:

***answer in significant digits

Answer 1

Solution:

Given: The ball’s initial horizontal velocity v_x = 8 m/s and Initial vertical speed v_y = 6 m/s

a) The ball’s horizontal speed 0.5 seconds into its flight is: 8 m/s.

Because there is no acceleration in the horizontal direction, thus there no change in the ball’s horizontal speed during entire motion of the ball.

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b) The ball’s horizontal speed midway through its flight is: 8m/s

Because there is no acceleration in the horizontal direction, thus there no change in the ball’s horizontal speed during entire motion of the ball.

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c) The ball’s horizontal speed immediately before contact with the ground is: 8 m/s

Because there is no acceleration in the horizontal direction, thus there no change in the ball’s horizontal speed during entire motion of the ball.

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d) The ball’s vertical displacement up is (circle one) greater than/less than/the same as the

vertical displacement down because: the height reached by the ball and the height fallen by the ball are same.

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e) The ball’s vertical velocity halfway through its flight is: 0 m/s

because: at the halfway through its flight the ball is at the maximum height where the vertical speed is momentarily zero.

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f) The ball’s vertical speed immediately before contact with the ground is: 8 m/s

because: the ball’s vertical speed decreases as it undergoes deceleration during the half of its motion; and the ball’s vertical speed increases by same amount as it undergoes acceleration during the second half of its motion. The net result is that it has same speed but only direction has reversed.