Class Management Help HW 7 Begin Date: 1/19/2017 12:01:00 AM Due Date: 4/5/2017

Question

Class Management Help HW 7 Begin Date: 1/19/2017 12:01:00 AM Due Date: 4/5/2017 11:59:00 PM End Date: 5/31/2017 10:00:00 AM (7%) Problem 6: A child throws a a penny off of the Eiffel tower (h 324 m) with a downward velocity of magnitude Va-Is m/s. next part 33% Part (a) Select from below the correct expression for the time t, it takes for the penny to reach the ground. Neglect air resistance. Final Correct Answer Student Answer Grade 100% 29h Grade Detail Feedback Student Final Answer Credit Submission History Totals Hints Totals the penny to fall the drop A 33% Part Calculate the time in seconds, that it takes for vo and 33% Part (c) Find the speed at which the penny strikes the ground v in meters per second, using the initial velocity, distance, h. All eweleer c 2017 TA, LLC

Explanation / Answer

a)from the eqn of motion

S = ut + 1/2 at^2

In this case, S = h ; u = v0 ; a = +g

h = v0 t + 1/2 g t^2

1/2 g t^2 + v0 t - h = 0

this is a quadratic eqnation that gives

t = -v0 + sqrt (v0^2 - 4 x 1/2 g (-h))/2 x 1/2 g

t = [sqrt(v0^2 + 2 g h) - v0]/g

b)using the formula we have derived in (a)

t = [sqrt(v0^2 + 2 g h) - v0]/g

t = [sqrt(18^2 + 2 x 9.8 x 324)- 18]/9.8 = 6.49 s

Hence, t = 6.5 s

c)from eqn of motion

v = u + at

v = vf ; u = v ; a = +g = 9.8 ; t = 6.5 s

vf = 18 + 9.8 x 6.5 = 81.7 m/s

Hence, v = 81.7 m/s

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