# Practice Test: Question Set - 21

**1. If**

*u*_{1}and*u*_{2}are the velocities of two moving bodies in the same direction before impact and*v*_{1}and*v*_{2}are their velocities after impact, then coefficient of restitution is given by- (A)

*(v*

_{1}- v_{2})/(u_{1}- u_{2})- (B)

*(v₂ - v₁)/(u*

_{1}- u_{2})- (C)

*(u*

_{1}- u_{2})/(v_{1}- v_{2})- (D)

*(u₂*+

*u₁)/(v₂*+

*v₁)*

**2. Work done is said to be zero, when**

- (A) Some
force acts on a body, but displacement is zero

- (B) No
force acts on a body but some displacement takes place

- (C) Either (A)
or (B)

- (D) None of the
above

**3. The range of projectile on a downward inclined plane is ________ the range on upward inclined plane for the same velocity of projection and angle of projection.**

- (A) Less than

- (B) More
than

- (C) Equal to

- (D) None of
These

**4. The point, through which the whole weight of the body acts, irrespective of its position, is known as**

- (A) Moment
of inertia

- (B) Center of gravity

- (C) Center of percussion

- (D) Center of mass

**5. The total energy possessed by a system of moving bodies**

- (A) Is
constant at every instant

- (B) Varies
from point to point

- (C) Is
maximum in the start and minimum at the end

- (D) Is
minimum in the start and maximum at the end

**6. The acceleration of a body sliding down an inclined surface is**

- (A)

*g*

*sinθ*

- (B)

*g*

*cosθ*

- (C)

*g*

*tanθ*

- (D) None of
these

**7. A force while acting on a body may**

- (A) Change
its motion

- (B) Balance the
forces, already acting on it

- (C) Give rise to
the internal stresses in it

- (D) All of these

**8. A machine having an efficiency less than 50%, is known as**

- (A) Reversible
machine

- (B) Non-reversible
machine

- (C) Neither
reversible nor non-reversible machine

- (D) Ideal
machine

**9. Static friction is always __________ dynamic friction.**

- (A) Equal to

- (B) Less than

- (C) Greater than

- (D) None of
these

**10. In the shown figure, the tension (**

*T*) in the string will be- (A)

*m₁. m₂. g/(m₁*+

*m₂)*

- (B) 2

*m₁. m₂. g/(m₁*+

*m₂)*

- (C)

*(m₁*+

*m₂)/ m₁. m₂. g*

- (D)

*(m₁*+

*m₂)/*2

*m₁. m₂. g*

**11. 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)*

**12. A smooth cylinder lying on a __________ is in neutral equilibrium.**

- (A) Curved
surface

- (B) Convex
surface

- (C) Horizontal
surface

- (D) None
of these

**13. The unit of energy in S.I. units is**

- (A) Dyne

- (B) Watt

- (C) kg-m

- (D) Joule

**14. A ladder is resting on a rough ground and leaning against a smooth vertical wall. The force of friction will act**

- (A) Downward at
its upper end

- (B) Upward
at its upper end

- (C) Zero
at its upper end

- (D) Perpendicular
to the wall at its upper end

**15. The periodic time of one oscillation for a simple pendulum is (where**

*l*= Length of the pendulum.)- (A)

*(1/2π). √(l/g)*

- (B)

*(1/2π). √(g/l)*

- (C) 2

*π. √(l/g)*

- (D) None of
these

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