Lenny wrote the steps he used to find the mass of an object with 400 j of energy moving at a velocity of 8 m/s.

1. find the square of 8 m/s, which is 64 m2/s2.
2. divide kinetic energy, 400 j, by 64 m2/s2, which is 6.25 j per m2/s2.
3. divide 6.25 j per m2/s2 by 2 to get a mass of 3.125 kg.

which best describes lenny’s error?

in step 1, he should have found the square root of 400 j instead of squaring 8 m/s.
in step 1, he should have multiplied 8 m/s by 2 instead of squaring it.
in step 2, he should have divided 64 m2/s2 by 400 j instead of dividing 400 j by 64 m2/s2.
in step 3, he should have multiplied 6.25 j per m2/s2 by 2 instead of dividing it by 2.

Adiver in midair has an angular velocity of 6.0 rad/s and a moment of inertia of 1.2 kg·m2. he then pulls is arms and legs into a tuck position and his angular velocity increases to 12 rad/s. the net external torque acting on the diver is zero. what is his moment of inertia in the tuck position?

Aball tossed vertically upward from the ground next to a building passes the bottom of a window 1.8 s after being tossed and passes the top of the window 0.20 s later. the window is 2.0 m high from top to bottom. what was the ball's initial velocity? the unit vector j^ is directed upward. how far is the bottom of the window from the launch position? how high does the ball rise above the launch position?

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