 # Describe - Practice questions and answers for AS Physics A

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## Describe - Practice Questions and answers for AS Physics A OCR - Mechanics G481 1605 22 0  Created by nikeishabk over 5 years ago
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Derive and Apply - Practice Questions and answers for AS Physics A OCR - Mechanics G481
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 Question Answer Describe an experiment to determine the acceleration of free fall g using a falling body. Measurements: Height (distance) Time (of fall) Instruments: Stop watch/timer/clock/video Ruler/tape (measure) Calculation: g = 2s/t2 or g = 2 gradient of . s-t2 graph g is an estimate: air resistance / drag parallax (landing time) starting/stopping the clock ((v+u)/t = s/t, v=u+at, u=0) (s=ut+1/2at^2 (ut=0), s = at^2/2, a(g)=2s/t^2). Describe the motion of bodies falling in a uniform gravitational field with drag. Acceleration: Terminal velocity: Net / total / resultant force (on drop) is zero ‘upward force = downward force’ / ‘weight = drag’ / ‘weight balances drag’ Describe a simple experiment to determine the centre of gravity of an object. Suspend object from a point and then) mark a vertical line on the object Plumb line / ‘pendulum’ (used to find the vertical line) Hang from another point / place (and draw another vertical line) (wtte) Where the lines intersect gives position of centre of gravity (wtte). Describe the factors that affect thinking distance and braking distance. speed, mass, condition of tyres/tread, condition of brakes, condition of road (surface), gradient of road For each factor, correct description of how braking distance is affected : Greater speed means greater distance OR distance ∝ speed2 Greater mass means greater distance OR distance ∝ mass Worn tyres / brakes implies less friction therefore greater distance Bald tyres Wet / slippery / icy road means less friction therefore greater distance Uphill means shorter distance. Describe and explain how air bags, seat belts and crumple zones in cars reduce impact forces in accident. Prevent collision with steering wheel / windscreen /dashboard Time for stopping is more / distance for stopping is more / seat belt ‘stretches’ Smaller deceleration / acceleration (of person) Reference to K.E.=Fs or ½ mv^2=Fs. Describe how air bags work, including the triggering mechanism. Large deceleration / rapid decrease in speed (triggers the air bag). Describe how the trilateration technique is used in GPS. (Several) satellites used Distance from (each) satellite is determined. Time taken for signal to travel from satellite to car/‘delay’ time for signal is determined. Distance = c x ‘delay’ time Position / distance is determined using c / speed of e.m waves / radio waves / microwaves and delay time Trilateration is used to locate the position of the car OR position of car is where circles/spheres cross/intersect. Describe the behaviour of springs and wires in terms of force, extension, elastic limit, Hooke’s law and the force constant (ie force per unit extension or compression). Measurement: original / initial length (Not: final length) extension / initial and final lengths, weight / mass Equipment: Micrometer / vernier (calliper) (for the diameter of the wire) Ruler / (metre) rule / tape measure (for measuring the original length / extension) Travelling microscope (for measuring extension) Scales / balance (for measuring the mass & mg equation is used or for measuring weight) / Newton meter (for the weight of hanging masses) / ‘known’ weights used. Describe an experiment to determine the Young modulus of a metal in the form of a wire. Capture.JPG (image/JPG) Describe the shapes of the stress against strain graphs for typical materials. Capture.JPG (image/JPG)