The following is the distance-time table on an object in motion: Time in seconds Distance in meters 0 0 1 1 2 8 3 27 4 64 5 125 6 216 7 343 What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?

From the given table it is clear that the distance travelled S by the object is equal to the cube of the time taken t for covering that distance. Therefore, S ∝ t 3 We know that the velocity, v = S t and acceleration, a = v t . Therefore, a = S t 2 = t 3 t 2 = t . So we can conclude that the acceleration is increasing with time.

The following is the distance-time table on an object in motion: Time in seconds Distance in meters 0 0 1 1 2 8 3 27 4 64 5 125 6 216 7 343 What do you infer about the forces acting on the object?

From the given table it is clear that the distance travelled S by the object is equal to the cube of the time taken t for covering that distance. Therefore, S ∝ t 3 We know that the velocity, v = S t and acceleration, a = v t . Therefore, a = S t 2 = t 3 t 2 = t . So we can conclude that the acceleration is increasing with time. As the force, F = ma , where m is the mass, we can conclude the force is increasing at a constant rate.

A motor car of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km h - 1 . Its velocity is slowed down to 36 km h - 1 in 4 seconds by an unbalanced force. Calculate the acceleration and change in momentum. Also calculate the magnitude of force required.

Given that, Mass of the car, m = 1200 kg Initial velocity, u = 90 km h - 1 = 90 × 5 18 m s - 1 = 25 m s - 1 Final velocity, v = 36 km h - 1 × 5 18 m s - 1 = 10 m s - 1 Time taken for the velocity change, t = 4 s We know that, v = u + at , where a is the acceleration. Therefore, 10 = 25 + a × 4 a = - 15 4 = 3 . 75 m s - 2 Initial momentum of the car, p i = mu = 1200 × 25 = 30 , 000 kg m s - 1 Final momentum of the car, p i = mv = 1200 × 10 = 12 , 000 kg m s - 1 Change in momentum, Δp = p f - p i = 12 , 000 - 30 , 000 = - 18000 kg m s - 1 We also know that, the force is rate of change of momentum, F = Δp t = - 18000 4 = - 4500 N

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IMPORTANT

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To study the third law of motion, the following sets of apparatus are available in a laboratory.

Set (i) One spring balance, two weight boxes, inextensible thread, one pulley with a clamp, two pans of known mass.

Set (ii) Two identical spring balances, one weight box, inextensible thread, one frictionless pulley with a clamp, one pan of known mass, rigid support.

Set (iii) Four identical spring balances, two pulleys, inextensible thread, two clamps, two pans of known masses, two rigid support.

Set (iv) Two identical spring balances, two weight boxes, two rigid supports, two pans of known masses, inextensible thread, two frictionless pulleys with clamps.

To perform the experiment successfully by using minimum apparatus, the best choice would be:

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Important Questions on Force and Laws of Motion

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9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>Summative Assessment Some Solved CBSE Sample Questions>Q 28

For doing the experiment "to study the third law of motion using two spring balances", four students A, B, C and D set up their apparatus as shown below. The best setup is that of student.

(A)

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(B)

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(C)

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(D)

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9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>Summative Assessment Some Solved CBSE Sample Questions>Q 29

A man is lying down on a soft bed, which has sagged under his weight. Which of the following statements is correct?

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9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>HOTS Higher Order Thinking Skill & Brain Twisting>Q 1

A body is left from the point $A$ and allowed to move along the path $ABCD$ which is smooth. The thin arrow represents velocity and the thick arrow represents acceleration. What is wrong with one of the arrow?

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9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>HOTS Higher Order Thinking Skill & Brain Twisting>Q 2

The following is the distance-time table on an object in motion:

Time in seconds	Distance in meters
$0$	$0$
$1$	$1$
$2$	$8$
$3$	$27$
$4$	$64$
$5$	$125$
$6$	$216$
$7$	$343$

What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?

MEDIUM

9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>HOTS Higher Order Thinking Skill & Brain Twisting>Q 2

The following is the distance-time table on an object in motion:

Time in seconds	Distance in meters
$0$	$0$
$1$	$1$
$2$	$8$
$3$	$27$
$4$	$64$
$5$	$125$
$6$	$216$
$7$	$343$

What do you infer about the forces acting on the object?

MEDIUM

9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>HOTS Higher Order Thinking Skill & Brain Twisting>Q 3

Two persons manage to push a motorcar of mass

1200 kg

at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of

0.2 m s^{- 2}

. With what force does each person push the motorcar? (Assume that all persons push the motorcar with the same muscular effort.)

MEDIUM

9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>HOTS Higher Order Thinking Skill & Brain Twisting>Q 4

A hammer of mass

500 g

, moving at

50 m s^{- 1}

, strikes a nail. The nail stops the hammer in a very short time of

0.01 s

. What is the force of the nail on the hammer?

MEDIUM

9th CBSE

IMPORTANT

Modern's abc+ Of Science - Physics For Class IX>Chapter 2 - Force and Laws of Motion>HOTS Higher Order Thinking Skill & Brain Twisting>Q 5

A motor car of mass

1200 kg

is moving along a straight line with a uniform velocity of

90 km h^{- 1}

. Its velocity is slowed down to

36 km h^{- 1}

4

seconds by an unbalanced force. Calculate the acceleration and change in momentum. Also calculate the magnitude of force required.

Important Questions on Force and Laws of Motion

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