Chp. 9-13 Part I. Multiple Choice (2 points each) 1. To change the total (linear

Question

Chp. 9-13 Part I. Multiple Choice (2 points each) 1. To change the total (linear) momentum of a system. a. the net internal force acting on the system must be non-zero. b. the net external force acting on the system must be non-zero c. (Momentum is always conserved.) 2. To change the mechanical energy (K+U of a system, a. non-conservative forces must do work. b. conservative forces must do work. c. (Mechanical energy is always conserved.) 3. the between two masses is increased, the magnitude of the gravitational force When distance they exert on each other a. decreases. b. increases. c. doesn't change. 4. When the distance between two masses is increased, what happens to their gravitational potential energy? a. U decreases b. U increases. c. U doesn't change. 5. Three forces are applied to the corner of a wooden square. All three forces have the same magnitude, and all three lie in the plane of the board. Compare the magnitudes of the three torques about point O. 6. A projectile is fired upward an initial velocity equal to its escape velocity. What can you say about its energy? a. K> 0, U> 0, E 0 b. K 0, U 0 c. K> 0, U

Explanation / Answer

1. delta (p)=p2-p1

=integration (Fdt)

so the external force must be non-zero

2.a non-conservative force changes the mechanical energy since kinetic friction is a non conservative force which reduces the mech. energy

3 F=g*(( m1*m2)/(r^2))

distance r increased F decreases as Gravitational force is inversely proportional to distance

4 gravitational potentail Energy U = -GMm/d this means when distance d increases the U becomes less negative so it increases

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