Please check to see if my calculations are correct. I am unsure if I used the right values and setup.(adsbygoogle = window.adsbygoogle || []).push({});

You throw a rock of weight 21.0 N vertically into the air from ground level. You observe that when it is a height 14.8 m above the ground, it is traveling at a speed of 25.7 m/s upward.

a. Use the work-energy theorem to find its speed just as it left the ground;Take the free fall acceleration to be g = 9.80 m/s^2 .

m_rock = 21.0 N/ 9.8 m/s^2 = 2.14285 kg

F*d = 0.5*m*(v_2)^2 - 0.5*m*(v_1)^2

14.8 m*(-21 N) - 0.5*m*(v_2)^2 = -0.5*m*(v_1)^2

v_1 = sqrt[(F*d - 0.5*m_rock*(v_2)^2)/(-0.5*m_rock)]

= sqrt[((14.8m*-21.0N) - 0.5*2.14 kg*(25.7 m/s)^2)/(-0.5*2.14 kg)]

= 30.8 m/s ??

b. Use the work-energy theorem to find its maximum height.

Take the free fall acceleration to be g = 9.80 m/s^2 .

F*d = 0 - 0.5*m*(v_1)^2

d = [- 0.5*m*(v_1)^2]/[F] = 0.5*(v_initial)^2/g

For v_initial ,am I supposed to use the value that I found in Part A?

d = 0.5*(30.8 m/s)^2/g = 48.4 m ??

Thanks.

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# Homework Help: Work-Energy Theorem calculations

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