The friction experienced by a body, when at rest, is known as

The dynamic friction is the friction experienced by a body, when the body

A

is in motion

B

is at rest

C

just begins to slide over the surface of the other body

D

none of the mentioned

The change in length due to a tensile or compressive force acting on a body is given by (where P = Tensile or compressive force acting on the body, $$l$$ = Original length of the body, A = Cross-sectional area of the body and E = Young's modulus for the material of the body)

A

$$\frac{{{\text{P}}l{\text{A}}}}{{\text{E}}}$$

B

$$\frac{{{\text{P}}l}}{{{\text{AE}}}}$$

C

$$\frac{{\text{E}}}{{{\text{P}}l{\text{A}}}}$$

D

$$\frac{{{\text{AE}}}}{{{\text{P}}l}}$$

A body of weight 'W' is required to move up on rough inclined plane whose angle of inclination with the horizontal is 'α'. The effort applied parallel to the plane is given by (where μ = tanφ = Coefficient of friction between the plane and the body.)

A

P = W tanα

B

P = W tan (α + φ)

C

P = W (sinα + μcosα)

D

P = W (cosα + μsinα)

Coulomb friction is the friction between

A

Bodies having relative motion

B

Two dry surfaces

C

Two lubricated surfaces

D

Solids and liquids

A friction circle is a circle drawn when a journal rotates in a bearing. Its radius depends upon the coefficient of friction and the

A

Magnitude of the forces on journal

B

Angular velocity of journal

C

Clearance between journal and bearing

D

Radius of journal

For a shoe brake, the equivalent coefficient of friction is equal to (where $$\mu $$ = Actual coefficient of friction and $$\theta $$ = Semi-block angle)

A

$$\frac{{2\mu \sin \theta }}{{\theta + \sin \theta }}$$

B

$$\frac{{\mu \sin \theta }}{{2\theta + \sin 2\theta }}$$

C

$$\frac{{4\mu \sin \theta }}{{\theta + \sin \theta }}$$

D

$$\frac{{4\mu \sin \theta }}{{2\theta + \sin 2\theta }}$$

Dynamic friction as compared to static friction is

A

Same

B

More

C

Less

D

May be less of more depending on nature of surfaces and velocity

The radius of a friction circle for a shaft rotating inside a bearing is (where r = Radius of shaft and $$\tan \varphi $$ = Coefficient of friction between the shaft and bearing)

A

$${\text{r}}\sin \varphi $$

B

$${\text{r}}\cos \varphi $$

C

$${\text{r}}\tan \varphi $$

D

$$\frac{{\text{r}}}{2}\cos \varphi $$

The ratio of static friction to dynamic friction is always

A

Equal to one

B

Less than one

C

Greater than one

D

None of these

Static friction is always __________ dynamic friction.

A

Equal to

B

Less than

C

Greater than

D

None of these

The friction experienced by a body, when at rest, is known as

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