A physics student of mass mm = 100 kg gets a summer job painting houses. On his first project, he builds a platform using large pine board with a mass of mb = 60 kg The board has an overall length of L = 8.5 meters and set on two 1 meter tall saw horses so that l = 2.25 meters overhangs each side as shown above.
How far from the left end of the beam can the painter stand before the board (and painter) begin to tip over?
x = m
HELP: In order to unbalance the beam, the beam would lift up from the support at point A. Therefore, you should pivot about point B. Also, notice that if the board lifts up at point A, that the normal force at point A is zero.
HELP: Using the point B as the pivot, there are two forces that contribute to the torque, the force of the man's weight, and the force of the weight of the beam.
Later that day, after thinking about how cool rotational dynamics really is, the student decides to conduct an experiment. He removes one of the supports and places the other one 1/3 of the way from the left edge. Standing at the end of the board, he has his girl friend place paint cans, each of mass mc = 1.94 kg, on the opposite end. How many cans will the girl have to place on the board to provide the best balance? (You may neglect the small length of the board that both the man and the cans occupy. Assume both are points at the ends of the board.)
Number of cans = cans
HELP: For the board to remain stable, the torques all have to add up to zero. We could pick any point we wanted to to sum the torque, but some points might make the math easier. What would be a good point to sum the torques about?
HELP: How many forces are there causing torques?
3 answers
1 answer