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Circular Motion

The wheels on the bus go round and round, but can you name all the forces in a rotating reference frame? Learn to derive these and more through sheer force of reason in Circular Motion.

Circular Motion - Level 4 Challenges


A boy runs on a circular path of radius \( R=28\text{ meters}\) with constant speed \(u=4 \text{ m/s}\).

Another boy starts from the center of the circle to catch the first boy. The second boy always moves towards the first one. and maintains a speed of \(v = 4\text{ m/s}\). How long will the chase last in seconds?

Details and Assumptions:

1) Ignore air friction.

2) Take \(\pi = \dfrac{22}7\).

A small block can move in a straight horizontal line \(AB\).Flash lights from one side projects its shadow on a curved vertical wall which has a horizontal cross section as a circle. If tangential and normal acceleration of shadow of the block on the wall as a function of time can be represented as:

\[a_N=\frac{cvR}{(2Rt-vt^2)} \quad , \quad a_T=\frac{R(vt-R)v^{\frac{d}{e}}}{(2Rt-vt^2)^{\frac{f}{g}}}\].

Find \(|c|+|d|+|e|+|f|+|g|\)

Details and Assumptions

  • As shown in figure \(v\) is the constant along \(AB\).

  • Given Figure is top view of the setup.

  • \(c,d,e,f,g\) are natural numbers and \(\frac{d}{e} ,\frac{f}{g}\) are in simplest forms.

  • \(a_N,a_T \) represent normal and tangential accelerations respectively.

  • you can neglect minus sign in accelerations due to directions.

Consider a body, attached to a string of length \(r\), to be initially at rest in the vertical plane. It can be proved that if we give the body an initial velocity of \(v>\sqrt{5gr}\), then, the body can make complete revolutions in the vertical plane about the point of suspension.

Let us consider that the body, initially at rest, is given a velocity \(v<\sqrt{5gr}\). If at this value of \(v\) the body eventually hits the point of suspension then we can write:

\[ v^2 = (a+\sqrt{b})gr \; . \]

Find \(a\times b\).

A spherical ball of mass \(m\) is kept at the highest point in the space between two fixed concentric spheres \(A\) and \(B\) . The smaller sphere \(A\) has a radius \(R\) and the space between the two spheres has a width \(d\). The ball has a diameter very slightly less than \(d\) . All surfaces are frictionless. The ball is given a gentle push towards the right . The angle made by the radius vector of the ball with the upward vertical is \(\theta\). What is the total normal reaction force exerted by the spheres on the ball in terms of angle \(\theta\)?

A frictionless track consists of a horizontal part of unknown length, which connects to a vertical semicircle of radius r . An object, which is given an initial velocity v , is to move along the track in such a way that after leaving the semicircle at the top it is to fall back to its initial position. What should the minimum length of the horizontal part be '?


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