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  4 Circular Motion

Objective Questions 

  1. A stone at the end of a thread is whirled in a horizontal circle above the head. The speed of

rotation is increased until the thread breaks. The subsequent path of the stone is

A a horizontal circle

B a straight line along a radius of the circle

C a straight line tangential to the circle

D a parabola in the vertical plane

2. A mass m is at a distance r  from the centre of the turntable. The frequency of rotation of the

turntable is  f . What is the kinetic energy of the mass?

A 2 f 2mr 2 

B 2π f 2mr  

C 2π2 f 2mr 2 

D 4π f 2mr 2

3. The figure shows a passenger of mass m in the car of a roller coaster at the top of a circular

loop of radius r .

  The angular velocity of the car is ω  and the normal reaction of the car on the passenger is

 R. The passenger does not drop down because

A  R > mg 

B mr ω 2 > mg 

C  R > mr ω 2 

D mg >  R

  4. A pendulum bob of massm moves in a horizontal circle of radius of curvature r  on the outside

surface of a cone. The tension in the string is T  and the normal reaction of the surface on the

bob is  R.

Which of the following is the centripetal force?

A T  sin θ  –  R cos α 

B T  cos θ  –  R sin α 

C T  sin α  –  R cos θ  

D T  cos α  –  R sin θ  

ω  

O

T  R 

mg 

θ 

α 

QB AA STPM Phys V1 C4 4th indd 1QB AA STPM Phys V1 C4 4th.indd 1 3/7/2008 4:58:51 PM3/7/2008 4:58:51 PM

8/19/2019 4 Circular Motion

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  5. A coin is placed at a distance r   from the axis of rotation of a turntable. The frequency of

rotation of the turntable is increased until the coin starts to move relative to the turntable. The

frequency of rotation  f  when this occurs is noted. The experiment is repeated for different

values of r  and the corresponding values of  f  is noted.

Which of the graphs correctly represents the results of the experiment?

A C

B D

Structured Question 

  1. A washing machine has a cylindrical drum of radius of 30.0 cm and spins about its axis which

is horizontal. What is the minimum angular velocity of the drum, in revolutions per minute,

so that the clothes spinning in a vertical circle would not drop from the top of the circle?

Essay Question 

  1. The figure shows a Ferris wheel which has a diameter of 135 m. It takes 1.0 minute to complete

a revolution. A person of mass 52 kg takes a ride on the Ferris wheel.

(a) Calculate

(i) the angular velocity of the Ferris wheel

 (ii) the speed of a basket on the Ferris wheel.

(b) Show on a diagram, the forces on the person

(i) in the basket A

 (ii) in the basket B

  Hence, calculate the reaction of the basket on the person in each of the baskets A and B.

r 

0   f 

r 

0   f 

r 

0   f 

r 

0   f 

Basket B

Basket A

QB AA STPM Phys V1 C4 4th indd 2QB AA STPM Phys V1 C4 4th.indd 2 3/7/2008 4:58:53 PM3/7/2008 4:58:53 PM