A 1.0-kg object moving in a certain direction has a kinetic energy of 2.0 J. It

Question

A 1.0-kg object moving in a certain direction has a kinetic energy of 2.0 J. It hits a wall and comes back with half its original speed. What is the kinetic energy of this object at this point? A) 2.0J B) 1.0J C) 0.50 J D) 0.25 J E) 4.0 J A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, there is no appreciable air resistance. What is the speed of the bead at point C? A) 0 m/s B) 34 m/s C) 69 m/s D) 20 m/s E) We cannot solve this problem without knowing the mass of the bead. When a car of mass 1167 kg accelerates from 10.0 m/s to some final speed, 4.00 times 10^5 J of work are done. Find this final speed. A) 28.0 m/s B) 22.4 m/s C) 25.2 m/s D) 30.8 m/s What is the angular speed, in rad/s, of a flywheel turning at 813.0 rpm? A) 85.14 rad/s B) 13.53 rad/s C) 63.84 rad/s D) 95.33 rad/s

Explanation / Answer

6) k = 1/2mv^2 = 2

v = 2 m/s

if v = 1 m/s

k = 1/2*1*1 = 0.5 J

7) from conservation of energy

1/2m(v2^2-v1^2) = mgh1-mgh2

v2 = 34.4 m/s

8) w = k2-k1

k2 = 1/2mv1^2+w = 458350

v2 = 28.02 m/s

9) w = 813*2*3.14/60 = 85.1 rad/s

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