A particle moving in the xy -plane experiences a velocity dependent force F → = k υ y i ^ + υ x j ^ , where υ x and υ y are the x and y components of its velocity υ → . If a → is the acceleration of the particle, then which of the following statements is true for the particle ?

quantity υ → × a → is constant in time

F → arises due to a magnetic field

kinetic energy of particle is constant in time

quantity υ → . a → is constant in time

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A person is sitting in a lift accelerating upwards. Measured weight of person will be

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Important Questions on Laws of Motion

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A person is standing in an elevator. In which situation, he experiences weight loss ?

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

Two wooden blocks are moving on a smooth horizontal surface such that the block having mass $m$ remains stationary with respect to block of mass $M$ as shown in the figure below. The magnitude of the applied force $P$ is,

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A block of mass

M

placed inside a box descends vertically with acceleration

a

. The block exerts a force equal to one-fourth of its weight on the floor of the box. The value of

a

will be

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A particle moving in the

xy

-plane experiences a velocity dependent force

\vec{F} = k (υ_{y} \hat{i} + υ_{x} \hat{j})

, where

υ_{x}

and

υ_{y}

are the

x

and

y

components of its velocity

\vec{υ}

. If

\vec{a}

is the acceleration of the particle, then which of the following statements is true for the particle ?

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A boy is standing on a weighing machine inside a lift. When the lift goes upwards with acceleration

\frac{g}{4},

the machine shows the reading

50 kg .

wt. When the lift goes downward with acceleration

\frac{g}{4},

the reading of the machine in

kg

wt

. would be

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A ball is thrown upward with an initial velocity

V_{0}

from the surface of the earth. The motion of the ball is affected by a drag force equal to

m γ v^{2}

(where

m

is mass of the ball,

v

is its instantaneous velocity and

γ

is a constant). Time taken by the ball to rise to its zenith is:

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

When a lift of mass

800 kg

is ascending with an acceleration of

5 m s^{- 2}

, the tension in its cable will be

______

take

(g = 10 m s^{- 2})

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

Two horizontal forces

{\vec{F}}_{1}

and

{\vec{F}}_{2}

act on a ball of mass

8 kg

. The forces are such that

{\vec{F}}_{1} = (14 N) \hat{i}

and

|{\vec{F}}_{2}| = 20 N

. If the

x

component of velocity

(v_{x})

changes linearly by

3 m s^{- 1}

1 \sec

, the angle between two forces is

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A girl drops an apple from the window of a train which is moving on a straight track with speed increasing with a constant rate. The trajectory of the falling apple as seen by the girl is

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A plumb line is suspended from a ceiling of a car moving with horizontal acceleration

a

. What will be the angle of inclination with vertical?

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A body of mass

m

is moving in a straight line with momentum

p

. Starting at time

t = 0

, a force

F = a t

acts in the same direction on the moving particle during time interval of

T

. So that its momentum changes from

p

2 p

. The value of

T

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A particle is moving along the

x

-axis with its coordinate with time

t

given by

x (t) = 10 + 8 t - 3 t^{2} .

Another particle is moving along the

y

-axis with its coordinate as a function of time given by

y (t) = 5 - 8 t^{3} .

t = 1 s,

the speed of the second particle as measured in the frame of the first particle is given as

\sqrt{v} .

Then

v (i n m s^{- 1})

is ___________.

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

The force on a body of mass

1 kg

(20 \hat{i} + 10 \hat{j}) N

. If it starts from rest, then the position of the body at time

t = 2 s,

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A block

A

takes

2 s

to slide down a frictionless incline of

30 °

and length

l

, kept inside a lift going up with uniform velocity

v

. If the incline is changed to

45 °

, the time taken by the block, to slide down the incline, will be approximately:

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

When will a body of mass

20 kg

moving at

15 m s^{- 1},

subjected to a retarding force of

100 N

, come to rest?

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

The graph below shows the variation of a force $F$ with time $t$ on a body which is moving in a straight line. Dependence of force on time is $F \propto t^{n}$ . Initially body is at rest.

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If the speed of the object is $2 m / s$ at $3 s$ , then the speed at $4 s$ will be approximately (in $m / s$ )

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A ball of mass

0.45 kg

which is initially at rest is hit by a bat. The bat remains in contact with the ball for

3 \times 10^{- 3} s

. During this time period the force on the ball by the bat is given as

F (t) = [(α \times 10^{6}) t - (β \times 10^{9}) t^{2}] N

where

α

and

β

are constants. The ball's speed immediately as it loses contact with the bat is

20 m s^{- 1}

. The correct relation between

α

and

β

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A man weighing

60 kg

is in a lift moving down with an acceleration of

1.8 {ms}^{- 2}

. The force exerted by the floor on him is?

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

Two blocks

A

and

B

of masses

m_{A} = 1 k g

and

m_{B} = 3 k g

are kept on the table as shown in figure. The coefficients of friction between

A

and

B

0.2

and between

B

and the surface of the table is also

0.2 .

The maximum force

F

that can be applied on

B

horizontally, so that the block

A

does not slide over the block

B

is : [Take

g = 10 m / s^{2}

]

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Physics>Mechanics>Laws of Motion>Inertial and Non-inertial Frames of Reference

A rocket is fired vertically from the earth with an acceleration of 2g, where g is the gravitational acceleration. On an inclined plane inside the rocket, making an angle

θ

with the horizontal, a point object of mass m is kept. The minimum coefficient of friction

μ_{m i n}

between the mass and the inclined surface such that the mass does not move is:

A person is sitting in a lift accelerating upwards. Measured weight of person will be

Important Questions on Laws of Motion

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