[2 Mark Questions]

Question 12 Marks

Exercise Problem.

A racing car has a uniform acceleration of 4 ms–2. What distance it covers in 10 s after the start?

Answer

Given: acceleration = 4ms^{– 2}.
time = 10s and initial velocity = 0
Formula: s = ut + 1/2 at²
Solution:
distance covered s = 0 × t + 1/2 × 4 ms^{– 2} × (10 s)².
s = 1/2 × 4 ms^{– 2} × 100 s²
= 1/2 × 400m
= 200m

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Question 22 Marks

What is meant by uniform circular motion? Give two examples of uniform circular motion.

Answer

When an object moves with constant speed along a circular path, the motion is called uniform circular motion.
Ex. (i) Revolution of Earth around the Sun
(ii) Revolution of Moon around the Earth.

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Question 32 Marks

Is the uniform circular motion accelerated? Give reasons for your answer.

Answer

When an object is moving with a constant speed along a circular path, the velocity changes due to the change in direction. Hence it is an accelerated motion.

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Question 42 Marks

What do you understand about negative acceleration?

Answer

If v < u, i.e. if final velocity is less than initial velocity, the velocity decreases with time and the value of acceleration is negative. It is called negative acceleration. It is also called as retardation (or) deceleration.

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Question 52 Marks

Compare speed and velocity

Answer

S.No.	Speed	Velocity
1.	The rate of change of distance	The rate of change of displacement
2.	Scalar quantity	Vector quantity
3.	Speed $=\frac{\text { Distance travelled }}{\text { time taken }}$	Velocity $=\frac{\text { Displacement }}{\text { time taken }}$

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Question 62 Marks

What do you mean by uniform motion?

Answer

An object is said to be in uniform motion if it covers equal distances in equal intervals of time how so ever big or small these time intervals may be.

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Question 72 Marks

Distinguish distance and displacement.

Answer

S.No.	Distance	Displacement
1.	The actual length of the path traveled by a moving body irrespective of the direction	The change in position of a moving body in a particular direction
2.	Scalar quantity	Vector quantity

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Question 82 Marks

Define Acceleration.

Answer

Acceleration is the rate of change of velocity with respect to time or it is the rate of change of velocity in unit time. It is a vector quantity. The SI unit of acceleration is

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Question 92 Marks

What is the difference between uniform acceleration and non – uniform acceleration?

Answer

Uniform Acceleration
1. It is the acceleration in which the object changes its velocity with equal intervals of time.
2. eg. The motion of a ball rolling down.
Non – Uniform Acceleration
1. It is the acceleration in which the object changes its velocity with unequal intervals of time.
2. A car travels 2 km in 1st hour, 3 km in 2nd hour and 3.5 km in 3rd horn.

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Question 102 Marks

Give the formula for each.
(i) Relation between initial, final velocity, acceleration and displacement in a uniformly accelerated straight line motion.
(ii) Relation between initial, final velocity, acceleration & time in a uniformly accelerated straight line motion.
(iii) Relation between initial velocity, acceleration, displacement and time.

Answer

(i) Relation between initial, final Velocity, acceleration \& displacement in a uniformly accelerated straight line motion. $v^2=u^2+2 a s$
(ii) Relation between initial, final velocity, acceleration \& time in a uniformly accelerated straight line motion. $v=u+$ at
(iii) Relation between initial velocity, acceleration, displacement and time. $s=u t+1 / 2$ at $^2$

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Question 112 Marks

What do you infer if
(i) Distance – time graph is straight line.
(ii) Velocity time graph is curved.
(iii) Displacement time is zig zag.

Answer

(i) Speed is constant.
(ii) Acceleration is not uniform.
(iii) Non uniform velocity.

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Question 122 Marks

Define Average speed.

Answer

It is the total distance travelled divided by the total time taken to cover this distance.
\[
\text { Average speed }=\frac{\text { Total distance travelled }}{\text { total time taken }}
\]

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Question 132 Marks

Name the two quantities, the slope of whose graph gives (i) speed (ii) acceleration.

Answer

(i) Distance-Time
(ii) Speed - Time
Question 6.
Define Average speed.
Answer:
It is the total distance travelled divided by the total time taken to cover this distance.
\[
\text { Average speed }=\frac{\text { Total distance travelled }}{\text { total time taken }}
\]

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Question 142 Marks

When an object is thrown upwards, what is true of velocity and acceleration at the highest point of motion of the object?

Answer

Velocity becomes zero
Acceleration remains same as g.

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Question 152 Marks

What is centrifugal force? Give examples.

Answer

Force acting on a body away from the centre of circular path is called centrifugal force. Thus centrifugal force is in a direction opposite to the direction of centripetal force. Its magnitude is same as that of centripetal force.
Example : Spin dryer of a washing machine, ride on a merry-go-round.

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Question 162 Marks

Find the magnitude of centripetal force.

Answer

Consider an object of mass $m$, moving along a circular path of radius $r$, with a velocity $v_{\text {, }}$ its centripetal acceleration is given by $a=v^2 / r$
Hence, the magnitude of centripetal force is given by,
\[
\begin{array}{l}
F =\text { mass } x \text { centripetal acceleration } \\
F = mv ^2 / r
\end{array}
\]

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Question 172 Marks

What are centripetal acceleration and centripetal force?

Answer

When a body moves in a circular pattern the acceleration is directed radially towards the centre of the circle.
The force causing this acceleration is also directed towards the centre of the circle and it is called centripetal force.

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Science [2 Mark Questions]

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