Unit 3 – Laws of Motion
I. Multiple Choice Questions
1. When a car takes a sudden left turn in the curved road, passengers are pushed towards the right due to
(a) inertia of direction
(b) inertia of motion
(c) inertia of rest
(d) absence of inertia
Answer: a
2. An object of mass $m$ held against a vertical wall by applying horizontal force $F$ as shown in the figure.
The minimum value of force $F$ is (IIT JEE 1994)
(a) Less than $mg$
(b) Equal to $mg$
(c) Greater than $mg$
(d) Cannot determine
Answer: c
3. A vehicle is moving along the positive $x$ direction, if sudden brake is applied, then
(a) frictional force acting on the vehicle is along negative $x$ direction
(b) frictional force acting on the vehicle is along positive $x$ direction
(c) no frictional force acts on the vehicle
(d) frictional force acts in downward direction
Answer: a
4. A book is at rest on the table which exerts a normal force on the book.
If this force is considered as reaction force, what is the action force according to Newton’s third law?
(a) Gravitational force exerted by Earth on the book
(b) Gravitational force exerted by the book on Earth
(c) Normal force exerted by the book on the table
(d) None of the above
Answer: c
5. Two masses $m_1$ and $m_2$ are experiencing the same force where $m_1 < m_2$.
The ratio of their acceleration $\dfrac{a_1}{a_2}$ is
(a) 1
(b) less than 1
(c) greater than 1
(d) all the three cases
Answer: c
6. Choose appropriate free body diagram for the particle experiencing net acceleration along negative direction.
(Each arrow mark represents the force acting on the system)
Answer: c
7. A particle of mass $m$ sliding on the smooth double inclined plane (shown in figure) will experience
(a) greater acceleration along the path AB
(b) greater acceleration along the path AC
(c) same acceleration in both the paths
(d) no acceleration in both the paths
Answer: b
8. Two blocks of masses $m$ and $2m$ are placed on a smooth horizontal surface as shown.
If force $F_1$ is applied from the left and later force $F_2$ is applied from the right,
the ratio of forces acting at the interface is $F_1 : F_2$
(Physics Olympiad 2016)
(a) 1 : 1
(b) 1 : 2
(c) 2 : 1
(d) 1 : 3
Answer: c
9. Force acting on the particle moving with constant speed is
(a) always zero
(b) need not be zero
(c) always non-zero
(d) cannot be concluded
Answer: b
10. An object of mass $m$ begins to move on the plane inclined at an angle $\theta$.
The coefficient of static friction of inclined surface is $\mu_s$.
The maximum static friction experienced by the mass is
(a) $mg$
(b) $\mu_s mg$
(c) $\mu_s mg \sin\theta$
(d) $\mu_s mg \cos\theta$
Answer: d
11. When the object is moving at constant velocity on the rough surface,
(a) net force on the object is zero
(b) no force acts on the object
(c) only external force acts on the object
(d) only kinetic friction acts on the object
Answer: a
12. When an object is at rest on the inclined rough surface,
(a) static and kinetic frictions acting on the object is zero
(b) static friction is zero but kinetic friction is not zero
(c) static friction is not zero and kinetic friction is zero
(d) static and kinetic frictions are not zero
Answer: c
13. The centrifugal force appears to exist
(a) only in inertial frames
(b) only in rotating frames
(c) in any accelerated frame
(d) both in inertial and non-inertial frames
Answer: b
14. Choose the correct statement from the following
(a) Centrifugal and centripetal forces are action reaction pairs
(b) Centripetal force is a natural force
(c) Centrifugal force arises from gravitational force
(d) Centripetal force acts towards the centre and centrifugal force appears to act away from the centre in a circular motion
Answer: d
15. If a person moving from pole to equator, the centrifugal force acting on him
(a) increases
(b) decreases
(c) remains the same
(d) increases and then decreases
Answer: a
