With the numerical values presented in the problem statement at the beginning of

Question

With the numerical values presented in the problem statement at the beginning of the assignment, at what speed will the balls be going when they hit the ground? Select the best choice, and present your reasoning. (Hint: your solution to #4 may be useful.)

(a) 26.6 m/s (b) 21.6 m/s (c) 18.8 m/s (d) 2.71 m/s (e) 7.35 m/s (f) None of these

Which of the following expressions gives the change in velocity of the balls between times t1 and t2? Remember, as in earlier problems, g represents the magnitude of the acceleration of gravity. Present your reasoning.

(a)g(t1 +t2) (b)12g(t2 –t1) (c)12g(t1 –t2) (d)g(t1 –t2) (e)g(t2 –t1) (f) None of these.

How does the change in velocity of the balls from t0 = 0 to t1 = 1 sec compare with the change in velocity from t1 = 1 sec to t2 = 2 sec. Present your reasoning.

(a) It is less. (b) It is the same. (c) It is greater. (d) It depends on the object.

An object in free fall falls (from rest) a distance y during the first t seconds. How far does it fall during the first 3t seconds? Present your reasoning.

(a) y + 3 (b) 3y (c) y + 9 (d) 9y (e) 4y (f) Something else!

Explanation / Answer

Given that height from which they dropped is h = 36 m

initial velocity is u = 0 m/s

final velocity at the ground is v = sqrt(2*g*h) = sqrt(2*9.81*36) = 26.6 m/s

So the answer is a) 26.6 m/s

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at t1 sec

v1 = gt1

at t2 sec

v2 = gt2

then change in velocity is v2-v1 = g*(t2-t1)

so the answer is e) g*(t2-t1)

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from to=0 sec to t1 = 1 sec

then change in velocity is dV = g*(t1-to) = g

from t1 = 1 sec to t2 = 2sec

then dV = g*(2-1) = g

so the answer is b) it is the same

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in first t sec
y = 0.5*g*t^2

in first 3t seconds

y = 0.5*g*(3t)^2 = 9*y

So the answer is d) 9y

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