Motion - MCQ Test (22-11-2017) - Class 9 MCQ

Acceleration is a vector quantity.
Since retardation and force are related to acceleration.Therefore,they are vector quantities.

When a body moves in a uniform circular motion then the body has an accelerated motion. It is because of change in velocity due to continuous change in direction of motion.

The area under the velocity-time graph gives the displacement of the body. Which is equal to area of rectangle and area of triangle.

The slope of a distance-time graph gives instantaneous speed of the moving object. Instantaneous speed can be more or less than average speed.

When a body moves from one position to another,the shortest (straight line) distance between the initial position and final position of the body is known as its displacement. Its a vector quantity.

Displacement can be zero,less than the magnitude of distance but can never be more than the magnitude of distance covered.

180° plane angle is equal to π radian. It is used to represent circular motion of a moving body.

In speed-time graph, uniform acceleration is represented by straight line velocity increasing with time.

Those physical quantities that possess only magnitude are called scalar quantity. Distance is a scalar quantity, since direction is required to represent distance.

When a body moves with uniform speed, then the average speed is same as instantaneous speed. Average speed is calculated by dividing the total distance travelled with total time taken.

A body is travelling at a constant speed in a circular path. It has an inward radial acceleration. This kind of motion will produce centrifugal force.

A body can have zero velocity and still be accelerated or constant speed and still have varying velocity but a body cannot have a constant velocity and varying speed.

When a body changes its position with time, it is said that body is in motion. A body cannot be at rest and in motion at the same time. So, statement is false.

Speed = distance / time, here, distance = 100 m and time = 50 s. therefore, speed = 100 m/50 s = 2 m/s.

Uniform circular motion is a case of accelerated motion.When a body moves in a uniform circular motion then the body has an accelerated motion. It is because of change in velocity due to continuous change in direction of motion.The third equation of motion,v² = u²+ 2aS. In this equation of motion, time is not present.So, both the statements are true.

The graph shown above is not possible in case of velocity-time graph. Graph may be straight, curved but not completely circular.

A body moving with uniform motion, never changes it speed. So, the velocity of the body remain same after 10 second that is 10m/s.

Instantaneous speed of a vehicle is measured by speedometer. Instantaneous speed is the speed of the vehicle at particular interval of time.

In speed-time graph, uniform acceleration is represented by straight line velocity increasing with time.

Let the radius of circular path be r and 3r respectively.

Let the speed of first and second object be v₁ and v₂ respectively.

The length of the first track = 2πr

Time taken by the first object t = 2πr/v₁

The length of the second track  = 2π(3r)

     = 6πr

Time taken by the second object, t = 6πr/v₂

Time taken by both object are same

2πr/v₁ = 6πr/v₂

v₁ : v₂ = 1 : 3

• In the speed-time graph shown above, speed is decreasing with time. This type of graph is represented by constant retardation.

Distance travelled by a moving body can never be zero and negative.

When a body covers equal distance in equal interval of time. It is said to be moving with constant speed. This type of motion is called uniform motion.

In uniform circular motion the direction of the body continuosly changes and hence the velocity (speed) of the body also changes.

A body moving horizontally with acceleration in vertical direction. A body moving with constant acceleration but zero velocity but a body moving with a constant velocity will not have accelerated motion.

Distance covered (S) = ut + ½ at².
Here, a = 8 m/s², t = 20 s.
Therefore, S=0×20+1/2×8×20×20=1600m

SI unit of both speed and velocity is m/s. Although velocity is a vector quantity but speed is a scalar quantity.

A curved line in a speed-time graph means non-uniform motion. In speed-time graph, uniform motion is represented by straight line parallel to time zone.

In the distance-time graph shown above, the speed of object A is greater than speed of object B as the object A is covering more distance per unit time.

Average speed = Total distance travelled/Total time taken

distance= 1 m/s×3600sec = 3600 m,

Average speed = (3600 +3600)m/(3600 + 3600 +1200)sec = 7200 m/8400 sec = 0.86 m/s.

It can be also represented in km/h.

In km/h,the average speed of the man is 0.0516 km/h

The speed of train = 120 m /6 = 20 m/s.

Time taken to cross a 50 m long bridge = (120 m + 50 m)/20 = 170/20 = 8.5 second.