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**As the ball revolves faster, the angle increases **

Example: The Conical Pendulum As the ball revolves faster, the angle increases If the radius is 0.02 m and the angle equal 30° What’s the speed for a given angle?

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A worker drags(يجر) a crate along a rough, horizontal surface by pulling on a rope tied ربط) ) to the crate. the worker exerts a force of 300 N on the rope that is inclined 37° to the horizontal .If the mass of the crate is 60 kg , and the coefficient of kinetic friction is 0.3 , find the acceleration of the crate .

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**A 2-kg block is placed on top of a 5 – kg**

A 2-kg block is placed on top of a 5 – kg . A horizontal force of 40 N is applied to the 5- kg block.If the coefficient of kinetic friction between the 5-Kg and the surface is 0.2 , and assuming that the 2 –Kg block is in the verge of slipping , a): What is the acceleration of the system . What is the coefficient of static friction is

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A 3kg block starts from rest at the top of 30º incline and slides a distance of 2m down the incline in 1.5s. Find (a) the acceleration of the block, (b) the coefficient of kinetic friction between the block and the plane, (c) the friction force acting on the block, (d) the speed of the block after it has slid 2m.

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Given m = 3kg, θ = 30o, x =2m, t = 1.5s Xo=0 then x = 1/2at 2 2 = 1/2a (1.5)2 a = 1.78 m/s2

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mg sin30 - f = ma f = m (g sin30 -a) f = 9.37N N - mg cos30 = 0 N = mg cos30 f = 9.37N µk = f / N = 0.368 V2=v02+2a(x-x0) v2 = 0 + 2(1.78)(2) = 7.11 then v = 2.67m/s

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Problem: Forces are being applied to a box sitting on a surface with friction. Will the box move horizontally (along the surface)? F1=50N, F2=50N, Mass of the block 10kg, and µs=0.4. Find The Fn and Acceleration Hint: must be greater or equal to

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Problem: A 20 kg sled is being pulled across a horizontal surface at a constant velocity. The pulling force has a magnitude of 80.0 N and is directed at an angle or 30.0° above the horizontal. Determine the coefficient of kinetic friction.

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Centripetal Force If there is a centripetal acceleration, then the net force must also be a centripetal force:

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**Tangential and Radial acceleration**

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**Example: A car exhibits a constant acceleration of 0**

Example: A car exhibits a constant acceleration of m/s2 parallel to the roadway. The car passes over a rise in the roadway such that the top of the rise is shaped like a circle of radius 500 m. At the moment the car is at the top of the rise, its velocity vector is horizontal and has a magnitude of 6.00 m/s. What is the direction of the total acceleration vector for the car at this instant?

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If the angle between

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**EX 3 A ball tied the end of string 0**

EX 3 A ball tied the end of string 0.5 m in length swings in a vertical circle under the influence of gravity . When the string makes an angle θ= 20 degre with the vertical , the ball has a speed of 1.5 m/s . (a) Find the magnitude of the radial component of acceleration at this instant. (b) what is the magnitude of the tangential acceleration when θ= 20 degre. (c) find the magnitude and direction of the total acceleration a at θ= 20 degre.

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NOTE

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EX 1 :A Circular curve a road is designed for traffic moving at 60 km/hr without depending on the friction . If the radius of the curve is 80 m , what is the correct angle of the banking on the road . SOL Θ=19.136°

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The moon revolves about earth in an orbit of radius and makes on revolution in 27.3 days .Find the acceleration of the moon toward the earth

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Example (a) Calculate the centripetal force exert on a 1000 kg car that negotiates a 600 m radius curve at 20.0 m/s. (b) Assuming an unbanked curve, find the minimum static coefficient of friction between the tires and the road.

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**A flat (unbanked ) curve on a highway has a radius of 100 m**

A flat (unbanked ) curve on a highway has a radius of 100 m .if the coefficient of static –friction between the tries (اطار العجلة) and the road is What is the maximum speed with which the car will have in order to round the curve successfully

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**Problem: A particle moves in a circular path 0**

Problem: A particle moves in a circular path 0.4m in radius with constant speed. If the particle makes five revolution in each second of its motion, find (a) the speed of the particle and (b) its acceleration.

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Since r=0.4m, t=0.4 s

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Problem: A train slows down as it rounds a sharp horizontal turn, slowing from 90km/h to 50km/h in the 15s that it takes to round the bend. The radius of the curve is 150m. Compute the acceleration at the train.

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**Problem: I rotate a ball at an angle of 30o**

Problem: I rotate a ball at an angle of 30o. What is the centripetal acceleration? If the string is 1 meter long, how fast is it rotating?

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Problem Driving in your car with a constant speed of 12 m/s, you encounter a bump in the road that has a circular cross section, as indicated in the Figure. If the radius of curvature of the bump is 35 m, find the apparent weight of a 67-kg person in your car as you pass over the top of the bump. N mg a=v2/r

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