Unit D Practice Questions Problem 4: A boy carrics a 5.0 kg brick up to the top

Question

Unit D Practice Questions Problem 4: A boy carrics a 5.0 kg brick up to the top of a ledge that is 10 m above the ground. The boy then throws the brick vertically downward with an initial instantaneous cod 5.0m. The bnck mpacts the ground below, coming to rest after making a small indentation in the dart. Air resistance can be ignored in this problem A How much work was initially required to lift the brick from the ground up to the ledge? What energy transformationls) took place as this happened. Explain B. How much additional work was done by the boy in throwing the huall downward C. what aergy transformations occurred as the ball doiceaded towwd the ground? D. What was the speed of the hall just before impacting the ground? E. During the collision with the dirt, how much impulse was deliv cred to ball? Draw a force vs. time that is consistent with this information Label numerical values that are reasonable for the duration and peak force F. How much cnergy ended up being transformed to thermal cnargy? Explain GWhich of your answers to questions above (A, B.C and Di would rmain the same if the thrown brick had a mass of 10.0 kg with the same spcod of S.0 ms? Which ons wouild be diffcrent? Explain

Explanation / Answer

A: mgh = 5 (9.8) (10) = 490 J

Chemical energy produced in muscles gets converted to potential energy gained by brick

B: 1/2 mv^2= 0.5 (5) (5^2) = 62.5 J

C: Potential energy gets converted to kinetic energy

D: initial KE + Initial PE = final KE

62.5 +490 = 0.5 (5) v^2

v = 14.866 m/s apprx

E: impulse = 5 ( 14.866-0) =74.33 kg m/s

F: 62.5 +490

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