Q. A coffee filter of mass 1.4 grams dropped from a height of 3 m reaches the ground with a speed of 0.7 m/s. How much kinetic energy Kair did the air molecules gain from the falling coffee filter? Start from the Energy Principle, and choose as the system the coffee filter, the Earth, and the air.
Q. A small block is at rest on the floor at the front of a railroad boxcar that has length . The coefficient of kinetic friction between the floor of the car and the block is µk. The car, originally at rest, begins to move with acceleration a. The block slides back horizontally until it hits the back wall of the car. (Use L for , mu for µk, and a and g as appropriate in your equations.)
(a) At the moment it hits, what is its speed relative to the car?
(b) At the moment it hits, what is its speed relative to the Earth?