Engineering Mechanics

(^650) „„„„„ A Textbook of Engineering Mechanics
QUESTIONS

1. What is torque? Give an example of torque.


2. State the Newton’s Laws of Motion of Rotation.


3. Define mass moment of inertia and kinetic energy of rotation.


4. Derive a relation between torque and angular acceleration of a body rotating about an
   axis.


5. Prove that the pull in a string having a body tied to it and passing over a pulley,

P= 2

()

Img

mr +I

where I= Moment of inertia of the pulley,

m= Mass of the body, and

r= Radius of the pulley

6. A uniform disc of radius r is allowed to roll down a rough inclined plane whose angle of
   inclination with the horizontal is θ. Prove that the linear acceleration of the disc is given by :

a= 22

2

gsin

rk

r

θ

+

where k is the radius of gyration.

OBJECTIVE TYPE QUESTIONS

1. The units of torque, work and energy are same.
   (a)Yes (b)No


2. Which of the following statement is correct?
   (a) The moment of inertia of a thin circular ring of mass (M) and mean radius (r) is
   0.25 mr^2.
   (b) The flywheel is a wheel which is used in flying machines.
   (c) The units of kinetic energy of rotation and kinetic energy of translation are different.
   (d) All of them.
   (e) None of them.


3. The torque acting on a body of moment of inertia (I) and angular acceleration (α) is
   (a) Iα (b) Iα^2
   (c) 0.5 Iα (d) 0.5 Iα^2


4. If the moment of inertia (I) of a pulley is doubled, then the acceleration of a body tied to
   a string and passing over it is
   (a) Halved (b) Remains the same
   (c) Doubled (d) None of these


5. In order to increase the acceleration of a mass rolling down on a rough inclined plane
   (without slipping), we have to
   (a) Increase the mass of the rolling body
   (b) Increase the inclination of the plane
   (c) Both (a) and (b)

ANSWERS

1. (a) 2. (e) 3. (a) 4. (d) 5. (b)

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