(a) State the conditions for the equilibrium of a rigid body acted upon by parallel forces (b)(i) Describe an experiment, using the principle of moments, to determine the mass of a metre rule (ii) State two precautions necessary to ensure accurate results. (c) A bullet of mass 120g is fired horizontally into a fixed wooden block with a speed of 20ms. The bullet is brought to rest in the block in 0.1s by a constant resistance. Calculate the: (i) magnitude of the resistance; (ii) distance moved by the bullet in the wood.
Explanation
(a) - Sum of forces in one direction is equal to the sum of forces in opposite direction. - Sum of anti-clockwise moments about a point is equal to the sum of clockwise moment about the same point. (b) Diagram:
Method: Suspend the metre rule on a knife edge. Adjust its position until it balances horizontally. Note the balance point G. Then suspend a mass M on one side of the rule. Adjust the rule until it balances horizontally again. Read and record X and Y as in the diagram above. According to the principle of moment: Mgx = Mgy m = m = mass of rule Precautions - Avoid drought - Avoid parallax in reading the metre rile
(c)(i) Deceleration a = = 200ms Resistance = ma = 0.12 x 200 = 24N (ii) Distance, s = 1.0m
