Motion (Test -1) - Class 9 Science, 21-02-2018 - Class 9 MCQ

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+ 2aSv²= 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.

The speed of the body moving on circular path is equal to 2πr/t. the ratio of speed of two body of radii 1x and 3x = 22πx/t : 2π3x/t = 1:3, so, none of the above statement is currect.

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

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.

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

In velocity-time graph, the body at rest cannot be represented by. So, graph will appear as in option C.

Average speed = Total distance travelled/Total time taken

distance= 1 m/s×36001 m/s×3600 sec = 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.

The motion of athletes is non-uniform. Displacement is a vector quantity. Negative acceleration is called as retardation, so SI unit of retardation is –ms-2.