Save 2.18.4 Submit 2.18.4 Section 23: Free-fall acceleration 2.23.2 A watermelon

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Save 2.18.4 Submit 2.18.4 Section 23: Free-fall acceleration 2.23.2 A watermelon cannon fires a watermelon vertically up into the air at a velocity of (1.50) +9.50 m/s, starting from an initial position 1.20 meters above the ground. When the watermelon reaches the peak of its flight, what is (a) its velocity, (b) its acceleration, (c) the elapsed time, and (d) its height above the ground? (a) 130 (02 submis sed) m/s (012 submissions used) m/s (0/2 submissions used) s (0/2 submissions used m Save 2.23.2Submit 2.23.2 2.23.3 A croissant is dropped from the top of the Eiffel Tower. The height of the tower is (1.50) 300.5 meters (ignoring the antenna, and this figure changes slightly with temperature). Ignoring air resistance, at what speed will the croissant be traveling when it hits the ground? (0/2 submissions used) m/s Save 2.23.3 Submit 2.23.3 Additional problems

Explanation / Answer

2.23.2   Given,

u = initial velocity = 9.50 m/s
hi = initial height = 1.20 m
g = acceleration due to gravity = 9.8 m/s^2

a) For any projectile, when an object reaches peak height, the velocity is 0 m/s

b) For any projectile, it's acceleration is always a constant -9.8 m/s^2 -- the acceleration due to gravity

c) We'll call the velocity at max height v - final velocity.

We can use this kinematics equation to get the elapsed time:

v = u - gt

Final velocity = initial velocity - gravity*time

0 = 9.5 - 9.8t

t = 9.5/9.8

= 0.97 s

d) To find its final height- it's max height above the ground- we can use this kinematics equation.

v^2 = u^2 - 2*g*delta(h)

delta(h) = (v^2 - u^2)/(2*9.8)

= (0 - 9.5^2)/(2*9.8)

= 4.60 m

But remember, we're not interested in the change in height (delta h), we're interested in the final height- h(f).

We know that,

delta(h) = hf - hi

hf = delta(h)+hi

= 4.60 + 1.2

= 5.80 m

2.23.3 By using equation of motion,

v^2 = u^2 + 2as

Where, v is final velocity

u is initial velocity

a is acceleration

s is distance

v = sqrt(0^2 + 2 * 9.8 * 300.5)

= 76.74 m/s

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