Two 4.0 kg blocks are tied together with a compressed springbetween them. They a

Question

Two 4.0 kg blocks are tied together with a compressed springbetween them. They are thrown from the ground with an initialvelocity of 35 m/s, 45(degrees) above the horizontal. At thehighest point of the trajectory they become untied and springapart. About how far below the highest point is the center of massof the two-block system 2.0s later, before either fragment hasd hitthe ground? The Answer is 20m . I keep getting 31m (which is wrong) how would you figure thisproblem ? the teacher suggested using formulas 4-26 and 4-25 from thetext book( Resnick) What are the steps to solving this problem and getting thecorrect answer? Two 4.0 kg blocks are tied together with a compressed springbetween them. They are thrown from the ground with an initialvelocity of 35 m/s, 45(degrees) above the horizontal. At thehighest point of the trajectory they become untied and springapart. About how far below the highest point is the center of massof the two-block system 2.0s later, before either fragment hasd hitthe ground? The Answer is 20m . I keep getting 31m (which is wrong) how would you figure thisproblem ? the teacher suggested using formulas 4-26 and 4-25 from thetext book( Resnick) What are the steps to solving this problem and getting thecorrect answer?

Explanation / Answer

I'm not sure what the two formulas are, but this problem is not ashard as it seems: As you probably have figured out, the highest point can be found bythe equation, vf2 =v02 + 2ad. vf is 0 at the highest point, and the acceleration is g, or 9.8.Therefore, you get v02 =19.6*d v0, the vertical velocity, can be found by trigonometry, 35 *sin(45) You get: 24.752 = 19.6 * d. Maximum distance = 31.25 This is the important part: the question asks for the distance ofthe center of mass from the highest point. The center of masscannot change due to internal forces. Therefore, you can treat thesystem as a single projectile. Solve for distance traveled in 2seconds. d = v0 * t + .5at2 Initial velocity is 0. d = .5at2 Plug in 2 for t and 9.8 for a. Distance from highest point = 19.6, or approximately20.

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