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3. Dynamics
A section of Physics, 9702
Listing 10 of 281 questions
The distance s moved by an object in time t may be given by the expression s = 1 2at 2 where a is the acceleration of the object. State two conditions for this expression to apply to the motion of the object. 1. 2. A student takes a photograph of a steel ball of radius 5.0 cm as it falls from rest. The image of the ball is blurred, as illustrated in . The image is blurred because the ball is moving while the photograph is being taken. cm initial position of ball in photograph cm cm final position of ball in photograph The scale shows the distance fallen from rest by the ball. At time t = 0, the top of the ball is level with the zero mark on the scale. Air resistance is negligible. Calculate, to an appropriate number of significant figures, the time the ball falls before the photograph is taken, time = s the time interval during which the photograph is taken. time interval = s The student in takes a second photograph starting at the same position on the scale. The ball has the same radius but is less dense, so that air resistance is not negligible. State and explain the changes that will occur in the photograph.
9702_s10_qp_22
THEORY
2010
Paper 2, Variant 2
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A sphere of radius R is moving through a fluid with constant speed v. There is a frictional force F acting on the sphere, which is given by the expression F = 6πDRv where D depends on the fluid. Show that the SI base units of the quantity D are kg m–1 s–1. A raindrop of radius 1.5 mm falls vertically in air at a velocity of 3.7 m s–1. The value of D for air is 6.6 × 10–4 kg m–1 s–1. The density of water is 1000 kg m–3. Calculate 1. the magnitude of the frictional force F, F = N 2. the acceleration of the raindrop. acceleration = m s–2 The variation with time t of the speed v of the raindrop in is shown in . v t State the variation with time of the acceleration of the raindrop. A second raindrop has a radius that is smaller than that given in . On , sketch the variation of speed with time for this second raindrop.
9702_s11_qp_22
THEORY
2011
Paper 2, Variant 2
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Questions Discovered
281