A 2.0 m long uniform plank of mass 8.0 kg rests horizontally on two small supports
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A 2.0 m long uniform plank of mass 8.0 kg rests horizontally on two small supports. Support S₁ is located 0.20 m from the left end of the plank, and support S₂ is located 1.60 m from the left end. A 60 N crate is placed on the plank at a point 1.30 m from the left end.
Assume all forces act vertically.
(a) Treating the plank as a rigid body, calculate the net torque produced by the plank’s weight and the crate’s weight about support S₁. Indicate the direction of the resulting torque.
(b) Calculate the net torque about support S₂ produced by the same two weights. Again, state the direction.
(c) Explain why the net torques you found in parts (a) and (b) are different even though the same forces act on the plank.
(d) If the crate is slowly slid toward the right end of the plank, determine algebraically the position at which the normal force at support S₁ becomes zero. Express your answer as the distance from the left end of the plank.