5. Class II lovers are designed to have(a) MAVR(b) MAVR(6) MAI(d) MA1Ans. MA >NUMERICALS1A crowbar of length 120 cm has its fulcrom statedat a distance of 20 cm from the load Calculate themechanical advantage of the crowbar Ans.2 A pair of scissors has its blades 15 cm long, whileits handles are 75 cm long. What is its mechanicalAn 0.53. A force or 5 kgf is required to cut a metal sheet. A pairof shears used for cutting the metal sheet has its blades5 cm long, while its handles are 10 cm long. Whateffort is needed to cut the sheet? Ans. 25 kgf4. Fig. 3.16 below shows a lever in use,(a) If a weight Wis placed ut odio of 250 cmfrom the support on the tower arm tonethe red, find wb) If a weight 5 kgf is kopt te balance the rod.find its position(c) To which class of lever does it belongAns.(*) 4 32 kgf (b) at dine 26 mfrom the support on longer am ) 13. A lever of length 9 cm has its ond arm 5 cm longand the effort arm is 9 cm long (a) To which candoes it belong? (b) Draw a diagram of the lever showingthe position of the futurum F and directions of boththe loud L and effort E. (c) What is the mechanicaladvantage and velocity ratio if the efficiency is 100%(d) What will be the mechanical advantage and velocityratio if the efficiency becomes 50%Ans.(a) class II (c) MA = 18. VR =(d) MA = 09. VR = 189. Fig. 3.17 below shows a lever in se 2018advantageFig. 3.16(a) To which class of lever does it belong?(b) If AB Im AF- 0.4 m, find its mechanicaladvantage(c) Calculate the value of E.Ans.(a) Class I (b) 15 (c) 10 kgf$. A man uses a crowbar of length 1.5 m to raise aload of 75 kgf by putting a sharp edge below the barat a distance of 1 m from his hand, (a) Draw adiagram of the arrangement showing the fulcrum (F).load (L) and effort (E) with their directions, (h) Statethe kind of lever. (c) Calculate (i) load arm,(ii) effort arm, (ii) mechanical advantage, and(iv) the effort needed.Ans. (b) class I (c) (i) 0.5 m (in) 1-0 mCili) 2 (iv) 37.5 kgf6. A pair of scissors is used to cut a piece of cloth bykeeping it at a distance of 80 em from its rivet andapplying an effort of 10 kgf by fingers at a distanceof 20 cm from the rivet(a) Find : (i) the mechanical advantage of thescissors, and (1) the load offered by the cloth(b) How does the pair of scissors act as a forcemultiplier or as a speed multiplier ?Ans.(a) (i) 0.25 ( 25 kgf. (b) speed multiplierA 4 m long rod of negligible weight is supported ata point 125 em from its one end and a load of18 kgf is suspended at a point 60 cm from thesupport on the shorter armFig. 3.17(a) To which class of levers does it belongs?(b) Without changing the dimensions of the lever.the load is shifted towards the fulcrum whathappens to the mechanical advantage of thelever?Ans. (a) It belongs to second class lever(b) The mechanical advantage of the lever will increasewhen load is shifted towards the folorum10. Fig. 3.18 below shows a wheel barrow of mass15 kg carrying a load of 30 kgf with its centre ofgravity at A. The points B and C are the centre ofwheel and tip of the handle sach that the horizontaldistance AB = 20 cm and AC = 40 cmС( 20cmFle. 3.18Find : (a) the load arm, (b) the effort arm, tc) themechanical advantage, and (d) the minimum effortrequired to keep the leg just off the groundAns. (a) 20 cm (b) 60 cm, (c) 3 (d) 15 kgf59