# CBSE Class 9th Science 8 – Motion MCQs

#### A train 50 m long passes over a bridge at a velocity of 30 km/h. If it takes 36 s to cross the bridge, then the lenA train 50 m long passes over a bridge at a velocity of 30 km/h. If it takes 36 s to cross the bridge, then the length of the bridge is ____ m.gth of the bridge is ____ m.

#### A body moves from A to B with a velocity of 20 m/s and comes back from B to A with a velocity of 30 m/s. The average velocity of the body during the whole journey is ____ m/s.

Average velocity is the rate of net displacement during the whole journey. As initial and final points are same, displacement is zero. Hence, average velocity of the body is zero.

#### The velocity-time graph for a body with non-uniform motion having constant acceleration is a ____.

The velocity-time graph for a body with non-uniform motion having constant acceleration is a straight line inclined to the time axis.

#### The rate of displacement is ____.

Rate of change of distance is speed while, rate of displacement is velocity.

#### Area under a velocity-time graph gives the ____ of the body.

Area under a velocity-time graph gives displacement of the body.

#### Speed of a body is always positive.

Speed is a scalar quantity. Hence, it is always positive

#### The velocity-time graph of a body with uniform velocity is a straight line ____.

When we say that body is moving with uniform velocity it means there is no acceleration. The slope of the velocity-time graph has zero degree inclination to the X-axis i.e., tanθ = tan0° = 0. Hence, the acceleration is zero and the velocity-time graph is parallel to the X-axis.

#### Unit of acceleration is m/s^{2}.

Unit of acceleration is m/s^{2}.

#### The ratio of total displacement to the total time taken by a body is equal to average speed.

The ratio of total displacement to the total time taken by a body is equal to average velocity

#### If a ball thrown up with a certain velocity attains a height of 40 m and comes back, then displacement of the ball is 80 m.

As initial position of the body when it starts its journey and final position of the body after its time of flight are same. Hence, the displacement of the ball is zero. Distance is the total length of the path which is 80 m.

#### SI unit for the average velocity is ____.

Average velocity is defined as the ratio of total displacement and total time taken. SI unit of average velocity is m/s.

#### When a body changes its position with respect to the surroundings, then it is said to be in motion.

When a body changes its position with respect to the surroundings, then the body is said to be in motion.

#### A train passes over a 400 m long bridge. If the speed of the train is 30 m/s and the train takes 20 s to cross the bridge, then the length of the train is ____ m.

The length of the train is 200 m.

#### Instantaneous speed of a vehicle is measured by ____.

Instantaneous speed of a vehicle is measured by speedometer.

#### An object can be at rest as well as in motion at the same time.

An object can be at rest relative to one object as well as in motion at the same time relative to another object.

#### A body in uniform circular motion has ____.

In uniform circular motion, the magnitude of velocity of the particle is constant, but its direction changes with time. Hence, a body in uniform circular motion has constant speed.

#### Velocity is the speed of an object moving in a definite direction. The velocity of an object can be uniform or variable.

Velocity is the speed of an object moving in a definite direction. The velocity of an object can be uniform or variable. It can be changed by changing the object’s speed, direction of motion or both.

#### Which of the following is a wrong statement regarding the graphical representation of motion of an object?

Cannot derive equations of motion

#### In the equation of motion, x = at + bt^{2}, the units of a and b are ____ respectively.

Unit of 'a' is m/s and 'b' is m/s^{2}.

#### If a body moves to and fro about a fixed point in regular intervals of time, then the body is said to possess ____ motion.

If a body moves to and fro about a fixed point in regular intervals of time, then the body is said to possess oscillatory motion.

#### Which of the following physical quantities is different from other physical quantities?

Average velocity is different because it is a vector physical quantity. Whereas, speed, distance and energy are scalar physical quantities.

#### The length of the actual path travelled by a body is known as displacement.

The length of the actual path travelled by a body is known as distance

#### Which of the following is incorrect?

As speed has only magnitude but no direction, it is a scalar quantity. Velocity, retardation, acceleration due to gravity and displacement has both direction as well as magnitude. Hence, they are vectors.

#### If the displacement-time graph of a particle represents a line parallel to the time-axis, then the velocity of the particle is ____.

The inclination of the displacement-time graph with time axis gives the magnitude of velocity. As the graph representing a line parallel to the time-axis, the velocity of the particle is zero.

#### A body moving with uniform acceleration 2 m/s^{2} covers a distance of 150 m in 10 seconds. Then, the initial velocity of the body is ____ m/s.

The initial velocity of the body is 5 m/s.

#### A body moving along a circular track of radius R completes one rotation in 2 seconds. Its average velocity in 2 second is ____ m/s.

The body completes one rotation in 2 second, so its displacement in 2 seconds is 0 m. Hence, the average velocity of the body in 2 seconds is 0 m/s.

#### The initial velocity of a body is 10 m/s. After 5 s, the velocity of the body is 20 m/s. Its velocity after 7 s is ____ m/s.

The initial velocity of a body is 10 m/s. After 5 s, the velocity of the body is 20 m/s. Its velocity after 7 s is ____ m/s.
A.18
B.24
C.16
D.27
Solution-
According to the problem,
initial velocity, u = 10 m/s
final velocity, v = 20 m/s
time duration, t = 5 s
Acceleration of the body is given by, a =v-u/t
a= 20 −10/ 5
a= 2 m/ s^{2}
So, the velocity after 7 s, is given by, v = u + at
v = 10 + 2 × 7
v = 24 m/s
v = 24 m/s

#### A particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle. Then, the velocity of the particle is constant.

When a force is applied perpendicular to the velocity of the body, then the motion of the body is circular due to change in its direction at every point. Hence, the body moves with a constant speed and variable velocity

#### Ratio of change in velocity to the time taken, for a body in motion is equal to its ____.

The ratio of change in velocity to the time taken, for a body in motion is equal to its acceleration.

#### If a body covers equal displacements in equal intervals of time then it is said to be moving with ____, however small these time intervals may be.

If a body covers equal displacements in equal intervals of time, then it is said to be moving with uniform velocity however, small these time intervals may be.

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