Chapter 5: Energy Q1-Consider the falling and rolling motion of the ball in the
ID: 1581904 • Letter: C
Question
Chapter 5: Energy Q1-Consider the falling and rolling motion of the ball in the following two resistance-free situations. In one situation, the ball falls off the top of the platform to the floor. In the other situation, the ball rolls from the top of the platform along the staircase-like pathway to the floor. For each situation, indicate what types of forces are doing work upon the ball Indicate whether the energy of the ball is conserved and explain why. Finally, fill in the blanks for the2-kg hall 02- Use the following diagram to answer questions #21-12.3 Neglect the effect of resistance forces. 2.1- As the object moves from point A to point D across the surface, the sum of its gravitational potential and kinetic energies a. decreases, only c. increases and then decreases 22-The object will have a minimum gravitational potential energy at point- b. decreases and then increases d. remains the same b. B c. C d. D e. E 2.3. The object's kinetic energy at point C is less than its kinetic energy at point a. A only b. A, D, and E cBonly d. D and E Q3- A rope is attached to a 50.0-kg crate to pull it up a frictionless incline at constant speed to a height of 3-meters. A diagram of the situation and a free-body diagram are shown below. Note that the force of gravity has two components (parallel and perpendicular component), the parallel component halances the applied force and the perpendicular component balances the normal force Source: physicsclassroom.comExplanation / Answer
1)
The only force doing work is gravity. Since it is an internal or conservative force, the total mechanical energy is conserved. Thus, the 100 J of original mechanical energy is present at each position. So the KE for A is 50 J.
The PE at the same stairstep is 50 J (C) and thus the KE is also 50 J (D).
The PE at zero height is 0 J (F and I). And so the kinetic energy at the bottom of the hill is 100 J (G and J).
Using the equation KE = 0.5*m*v2, the velocity can be determined to be 7.07 m/s for B and E and 10 m/s for H and K.
2.1)
The answer is D. The total mechanical energy (i.e., the sum of the kinetic and potential energies) is everywhere the same whenever there are no external or non-conservative forces (such as friction or air resistance) doing work.
2.2)
The answer is B. Gravitational potential energy depends upon height (PE=m*g*h). The PE is a minimum when the height is a minimum. Position B is the lowest position in the diagram.
2.3)
The answer is C. Since the total mechanical energy is conserved, kinetic energy (and thus, speed) will be greatest when the potential energy is smallest. Point B is the only point that is lower than point C. The reasoning would follow that point B is the point with the smallest PE, the greatest KE, and the greatest speed. Therefore, the object will have less kinetic energy at point C than at point B (only).
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