Laws of motion practice · Medium

A passenger in a moving bus is thrown forwards when the bus is suddenly stopped. This is explained by

A car of mass $M$ is moving with a uniform velocity $v$ on a horizontal road when the hero of a Hindi film drops himself on it from above. Taking the mass of the hero to be $m$, what will be the velocity of the car after the event?

A ball of mass $200 \mathrm{~g}$ rests on a vertical post of height $20 \mathrm{~m}$. A bullet of mass $10 \mathrm{~g}$, travelling in horizontal direction, hits the centre of the ball. After collision both travels independently. The ball hits the ground at a distance $30 \mathrm{~m}$ and bullet at a distance of $120 \mathrm{~m}$ from the foot of the post. The value of initial velocity of the bullet will be (if $g=10 \mathrm{~m} / \mathrm{s}^2$ )

Statement-I: Linear momentum of a body changes even when it is moving uniformly in a circle.
Statement-II: Force required to move a body uniformly along a straight line is zero.

Rocket propulsion is associated with

Consider a small block placed with zero velocity on a rough convey or belt moving with constant velocity. The block eventually comes to rest with respect to belt.
Statement-1: Net work done by kinetic friction on belt is zero.
Statement-2: The kinetic energy of the belt does not change.

A constant force acts on a body of mass ' ${m}$ ' at rest for ' $t$ ' sec and then ceases to act. In next ' $t$ ' sec, the body travels a distance ' $x$ '. Magnitude of force is

Given below are two statements:

Statement I: An elevator can go up or down with uniform speed when its weight is balanced with the tension of its cable.

Statement II: Force exerted by the floor of an elevator on the foot of a person standing on it is more than his/her weight when the elevator goes down with increasing speed.

In the light of the above statements, choose the correct answer from the options given below:

Consider the following statement:
When jumping from some height, you should bend your knees as you come to rest, instead of keeping your legs stiff. Which of the following relations can be useful in explaining the statement? Where symbols have their usual meanings.

Assertion: For the application of the second law of motion, there is no conceptual distinction between inanimate and animate objects.
Reason: An animate object needs an external force to accelerate.

The acceleration of an astronaut is zero once he steps out of his accelerated spaceship in the intersteller space. This statement is in accordance with

A piece of ice slides down a $45^{\circ}$ incline in twice the time it takes to slide down a frictionless $45^{\circ}$ incline. What is the coefficient of friction between the ice and incline?

A bird is sitting in a large closed cage which is placed on a spring balance. It records a weight of 25 N. The bird (mass m=0.5 kg) files upward in the cage with an acceleration of $2\;m/{s^2}$. The spring balance will now record a weight of

Frictional force that opposes relative motion between surfaces in contact is called ...X... and denoted by ...Y.... Here, X and Y refer to

A boy is standing in a lift moving upwards with constant acceleration. The boy throws a ball vertically up with initial velocity $u$ with respect to the lift and it reaches his hand just after time $t$. The upward acceleration of the lift is

In an air collision between an aeroplane and a bird, the force experienced by the bird as compared to that of the aeroplane is

Maximum speed of car for safe turning on horizontal road is

A body of mass $5 \mathrm{~kg}$ is acted upon by two perpendicular force $8 \mathrm{~N}$ and $6 \mathrm{~N}$, find the magnitude and direction of the acceleration.

A body is allowed to slide from the top along a smooth inclined plane of length 5 m at an angle of inclination $30^\circ$. If $g = 10\,m{s^{ - 2}}$, time taken by the body to reach the bottom of the plane is [in seconds]

A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring reads 49 N, when the lift is stationary. If the lift moves downward with an acceleration of $5\;m/{s^2}$, the reading of the spring balance will be

Maximum stress that can be applied to a wire which supports on elevator is $\sigma$. Mass of elevator is $m$ and it is moved upwards with an acceleration of $g / 2$. Minimum diameter of wire (Neglecting weight of wire) must be

A body of mass $5 \times 10^3 \mathrm{~kg}$ is launched upon a rough inclined plane making an angle of $30^{\circ}$ with the horizontal. Obtain the coefficient of friction between the body and the plane if the time of ascent is half of the time of descent.

A body of mass m is projected with a speed u making an angle $\alpha$ with the horizontal. The change in momentum suffered by the body along he y-axis between the starting point and the highest point of its path will be

Which one of the following statements is incorrect ?

STATEMENT-1 : It is easier to pull a heavy object than to push it on a level ground and

STATEMENT-2 : The magnitude of frictional force depends on the nature of the two surfaces in contact.

The limiting value of static friction between two surfaces in contact is

According to Newton's third law of motion, the action and reaction forces

A conveyor belt is moving at a constant speed of $4 \mathrm{~m} / \mathrm{s}$. A box is gently dropped on it. The coefficient of friction between them is $\mu=0.2$. The distance that the box will move relative to ground before coming to rest with respect to belt, is

If $\mu$, $R$ and $S$ represent coefficient of friction, normal reaction and distance moved. Then the general expression for work against friction

Assertion: Work done by force of friction in moving a body in any round trip is zero.
Reason: Frictional force is a conservative force.