Extra 1. A sport car has a maximum centripetal acceleration of 0.96g, the car can sustain without skidding out of a curv
Extra 1. A sport car has a maximum centripetal acceleration of 0.96g, the car can sustain without skidding out of a curved path. If the car is travelling at a constant 40ms-1 on a level ground. What is the radius of the tightest unbanked curve it can negotiate? (Ans: 170m)
1. ac=0.96g =0.96x9.8=9.408ms-2
v=40ms-1 r=?
2
v a c= r2 2 v 40 =170m r= ac 9.408
2. Passengers on a carnival ride move at constant speed in a horizontal circle of radius 5.0m making a complete circle in 4.0s. What is their acceleration? (Ans: 12ms-2)
Extra 2. r=5m For a complete circle,θ=2π rad,T=4 s ac=? ac=rω2
3. A centrifuge used to separate blood cells from blood plasma rotates at 55 rotations per second. What is the acceleration at the center of a centrifuge tube 8.0cm from the axis of rotations. (Ans: 9.55 x 103ms-2)
Extra 3. f = 55 rotations s-1 ,r = 8cm -2m =8x10 θ = 55 rev , t =1 s ac=? ac=r ω2 ac=r(2πf )2 ac= 8x10-2 x4xπ2x 552 ac=9.55x103
Machine [ What ?]
• That transmits force or torque to accomplish a definite purpose] [Why?]
The purpose of multiplying force
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• Do machines multiply work? (2012) • (Why a machine can’t multiplying energy?) A machine (1)Cannot supply more output energy than it is given as input energy (2)Output energy ≤ input energy (3)follows the law of conservation of energy 8
Functions of machine • To exert large force by application of a relatively small one e.g lever
• To convert a slow movement into a rapid one or vice versa e.g pully • To enable a force to be applied at a more convenient point e.g. forceps 9
The Effort ( Fi ) applied force to any machine. Fi= input force
The Load ( Fo ) exerted force by the machine. Fo = output force
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Mechanical Advantage ( MA) The ratio of load to effort
F load o MA effort F i
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Velocity ratio(VR) • The ratio of the distance moved by the effort to that moved by the load VR
s s
i
o
distance moved by the effort distance moved by the load
• Friction doesn’t alter VR • VR depends on geometric construction 12
