3+Dynamics

=Dynamics=

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=Resultant of 2 forces=

Example Question:
The diagram shows forces of magnitudes 20 N and 16 N inclined at 60°. (i) Calculate the component of the resultant of these two forces in the direction of the 20 N force. (ii) Calculate the magnitude of the resultant of these two forces. These are the only forces acting on a particle of mass 2 kg. (iii) Find the magnitude of the acceleration of the particle and the angle the acceleration makes with the 20 N force. media type="custom" key="14217220"

Example Answer:
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=Inlcined Plane= media type="custom" key="21016240"

Example Question:
A horizontal force of 24 N acts on a block of mass 12 kg on a horizontal plane. The block is initially at rest. This situation is first modelled assuming the plane is smooth. (i) Write down the acceleration of the block according to this model. Note - The next part of the question uses a constant resistance, not the usual F = muR The situation is now modelled assuming a constant resistance to motion of 15 N. (ii) Calculate the acceleration of the block according to this new model. How much less distance does the new model predict that the block will travel in the first 4 seconds? media type="custom" key="14218108" The 24 N force is removed and the block slides down a slope at 5° to the horizontal. The speed of the block at the top of the slope is 1.5 ms –1, as shown in the diagram. The answers to parts (iii) and (iv) should be found using the assumption that the resistance to the motion of the block is still a constant 15 N. (iii) Calculate the acceleration of the block in the direction of its motion. (iv) For how much time does the block slide down the slope before coming to rest and how far does it slide in that time? Note - The next part is tricky and now needs to use F = muR Measurements show that the block actually comes to rest in 3.5 seconds. (v) Assuming that the error in the prediction is due only to the value of the resistance, calculate the true value of the resistance. media type="custom" key="14218308"

Example Answer:
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=Pulleys= media type="youtube" key="wAjIZZ4axSY" height="450" width="600"

Here is an interactive pulley demonstration: media type="file" key="pulley.swf" width="692" height="603"

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=Pulley on Table=

Example Question:
A block of mass 4 kg slides on a horizontal plane against a constant resistance of 14.8 N. A light, inextensible string is attached to the block and, after passing over a smooth pulley, is attached to a freely hanging sphere of mass 2 kg. The part of the string between the block and the pulley is horizontal. This situation is shown in the diagram. The tension in the string is T N and the acceleration of the block and of the sphere is ams –2. (i) Write down the equation of motion of the block and also the equation of motion of the sphere, each in terms of T and a. [3] (ii) Find the values of T and a. [3] media type="custom" key="14216802"

Example Answer:
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=Towing= Here is an interactive demonstration of a towed object: media type="file" key="car_caravan.swf" width="705" height="570"