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Physics Part-I

Laws of motion

A man of mass 70 kg stands on a weighing scale in a lift which

Physics Part-I

Class 11

NCERT

Chapter 1: Physical World

16 questions

Chapter 2: Units and Measurements

51 questions

Chapter 3: Motion in Straight Line

50 questions

Chapter 4: Motion in a Plane

43 questions

Chapter 5: Laws of motion

52 questions

A bob of mass

0.1 k g

hung from the ceiling of a room by a string

2 m

long is set into oscillation. The speed of the bob at its mean position is

1 m s^{- 1}

.What is the trajectory of the bob if the string is cut when the bob is (a) at one of its extreme positions, (b) at its mean position.

A man of mass

70

k g

stands on a weighing scale in a lift which is moving.
(a) Upwards with a uniform speed of

10

m s^{- 1}

.
(b) Downwards with a uniform acceleration of

5

m s^{- 2}

.
(c) Upwards with a uniform acceleration of

5

m s^{- 2}

.
What would be the reading on the scale in each case?
(d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

Figure shows the position-time graph of a particle of mass

4 k g

. What is the (a) force on the particle for

t 4 s, 0 < t < 4 s

(b) impulse at t = 0 and t = 4 s? (Consider one-dimensional motion only).

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Chapter 6: Work, Energy and Power

41 questions

Chapter 7: System of Particles and Rotational Motion

45 questions

Chapter 8: Gravitation

33 questions

Question

Easy

Solving time: 2 mins

A man of mass $70$ $k g$ stands on a weighing scale in a lift which is moving.
(a) Upwards with a uniform speed of $10$ $m s^{- 1}$ .
(b) Downwards with a uniform acceleration of $5$ $m s^{- 2}$ .
(c) Upwards with a uniform acceleration of $5$ $m s^{- 2}$ .
What would be the reading on the scale in each case?
(d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

Views: 5,925 students

Updated on: Aug 29, 2022

Book:

Physics Part-I (NCERT)

Found 7 tutors discussing this question

Charlotte Discussed

A man of mass

70

k g

stands on a weighing scale in a lift which is moving.
(a) Upwards with a uniform speed of

10

m s^{- 1}

.
(b) Downwards with a uniform acceleration of

5

m s^{- 2}

.
(c) Upwards with a uniform acceleration of

5

m s^{- 2}

.
What would be the reading on the scale in each case?
(d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

6 mins ago

Discuss this question LIVE

6 mins ago

Text solutionVerified

(a)

. As the lift is moving at a uniform speed, acceleration

a = 0

R = m g = 70 \times 10 \Rightarrow 700 N

Reading on the weighing scale

= 700/ g = 700/10 = 70 k g

(b)

Mass of the man,

m = 70 k g

Acceleration,

a = 5 m / s^{2}

downward

Using Newtons second law of motion, we can write the equation of motion as:

R + m g = ma R = m (g - a) = 70 (10 - 5) = 70 \times 5 = 350 N

Reading on the weighing scale

\Rightarrow 350 g = 350/10 = 35 k g

(c)

Mass of the man,

m = 70 k g

Acceleration,

a = 5 m / s^{2}

upward

Using Newtons second law of motion, we can write the equation of motion as:

R - m g = ma R = m (g + a) = 70 (10 + 5) = 70 \times 15 = 1050 N

Reading on the weighing scale

\Rightarrow 1050/ g = 1050/10 = 105 k g

(d)

When the lift moves freely under gravity, acceleration

a = g

Using Newtons second law of motion, we can write the equation of motion as:

R + m g = ma R = m (g - a) = m (g - g) = 0

Reading on the weighing scale

= 0/ g = 0 k g

The man will be in a state of weightlessness.

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Practice more questions from Physics Part-I (NCERT)

A bob of mass

0.1 k g

hung from the ceiling of a room by a string

2 m

long is set into oscillation. The speed of the bob at its mean position is

1 m s^{- 1}

.What is the trajectory of the bob if the string is cut when the bob is (a) at one of its extreme positions, (b) at its mean position.

A man of mass

70

k g

stands on a weighing scale in a lift which is moving.
(a) Upwards with a uniform speed of

10

m s^{- 1}

.
(b) Downwards with a uniform acceleration of

5

m s^{- 2}

.
(c) Upwards with a uniform acceleration of

5

m s^{- 2}

.
What would be the reading on the scale in each case?
(d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

Figure shows the position-time graph of a particle of mass

4 k g

. What is the (a) force on the particle for

t 4 s, 0 < t < 4 s

(b) impulse at t = 0 and t = 4 s? (Consider one-dimensional motion only).

View all

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Question Text	A man of mass $70$ $k g$ stands on a weighing scale in a lift which is moving. (a) Upwards with a uniform speed of $10$ $m s^{- 1}$ . (b) Downwards with a uniform acceleration of $5$ $m s^{- 2}$ . (c) Upwards with a uniform acceleration of $5$ $m s^{- 2}$ . What would be the reading on the scale in each case? (d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?
Updated On	Aug 29, 2022
Topic	Laws of motion
Subject	Physics
Class	Class 11
Answer Type	Text solution:1 Video solution: 7
Upvotes	898
Avg. Video Duration	3 min

Text solutionVerified

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