Laws of motion practice · Mixed difficulty

A 60 kg man stands on a spring scale in the lift. At some instant he finds, scale reading has changed from 60 kg to 50 kg for a while and then comes back to the original mark. What should we conclude

A body of 5 kg is moving with a velocity of 20m/s. If a force of 100N is applied on it for 10s in the same direction as its velocity, what will now be the velocity of the body

For a system to follow the law of conservation of linear momentum during a collision , the condition is
Total external force acting on the system is zero.
Total external force acting on the system finite and time of collision is negligible.
Total internal force acting on the system is zero.

A particle moves in $x-y$ plane under the influence of a force $\overrightarrow{\mathrm{F}}$ such that its linear momentum is $\overrightarrow{\mathrm{P}}(\mathrm{t})=\hat{\mathrm{i}} \cos (\mathrm{kt})-\hat{\mathrm{j}} \sin (\mathrm{kt}).$ If $\mathrm{k}$ is constant, the angle between $\overrightarrow{\mathrm{F}}$ and $\overrightarrow{\mathrm{P}}$ will be:

Assertion: To conserve linear momentum of a system, no force should act on the system.

Reason: If net force on a system is zero, its linear momentum should remain constant.

A bird weighs 2 kg and is inside a closed cage of 1 kg. If it starts flying, then what is the weight of the bird and cage assembly

A car is negotiating a curved road of radius $120 \mathrm{~m}$. The road is banked at $7^{\circ}$. The coefficient of friction between the tyres and the road is $\mu_{\mathrm{s}}=\frac{1}{\sqrt{3}}$. The maximum safe velocity on the road in $\mathrm{m} / \mathrm{s}$ is $\left({g}=10 \mathrm{~m} / \mathrm{s}^2\right)$ :-

Assertion: A cricketer moves his hands forward to catch a ball so as to catch it easily without hurting.
Reason: He tries to decrease the distance travelled by the ball so that it hurts less.

Physical independence of force is a consequence of

A particle is moving in a circular path with a constant speed v. If $\theta$ is the angular displacement, then starting from $\mathrm{\theta } = 0^\circ$, the maximum and maximum changes in the momentum will occur, when value of θ is respectively

A body is moving on a horizontal surface. The force of friction acting between them is called

The force of kinetic friction does not depend on

If the resultant of all the external forces acting on a system of particles is zero, then form an inertial frame, one can surely say that

A uniform metre scale balances at the 40-cm mark when weights of 10g and 20g are suspended from the 10-cm and 20-cm marks respectively. The weight of the metre scale is

(A): A solid sphere and hollow sphere when released from the top of a smooth and fixed inclined plane, reach the ground simultaneously.
(R): Acceleration while sliding on a smooth inclined plane is independent of mass and dimension of the body.

A block of mass $m$ is placed on a rough horizontal surface. If $100 \mathrm{~N}$ of force is applied on it and it moves $10 \mathrm{~m}$. Then find the work done by friction on the block.

A rider on horse falls backward when horse starts running all of a sudden because of

A body is projected up a $45^{\circ}$ rough incline. If the coefficient of friction is 0.5 , then the retardation of the block is

particle moves in the X-Y plane under the influence of a force such that its linear momentum is $p\left( t \right) = A[\hat i\cos \left( {kt} \right) - \hat j\sin \left( {kt} \right)]$ where A and k are constant. The angle between the force and the momentum is

A ball is moving to and fro about the lowest point A of a smooth hemispherical bowl. If it is able to rise up to a height of 20 cm on either side of A, its speed at A must be $(Take\;g = 10\;m/{s^2},\;$ massof the body 5 g)

A Car takes a circular turn of radius 20 m at a speed of $54 \mathrm{~km} / \mathrm{h}.$ The least coefficient of friction between tyres and road that can prevent slide slipping is

Two bodies of masses 4 kg and 16 kg at rest to acted upon by same force. The ratio of times required to attain the same speed is

The propulsion of a rocket is based on the principle of conservation of

Assertion: Frictional forces are conservating forces.
Reason: Potential energy can be associated with frictional forces.

Given below are two statements: In the light
of the given statements, choose the correct
answer from the options given.

Statement I: Mass is a measure of inertia of the body.

Statement II: Greater the mass, greater is the force required to change its
state of rest or of uniform motion.

A body of mass M collides against a wall with a velocity V and retraces its path with the same speed. The change in momentum is [take initial direction of velocity as positive]

A wooden block of 90 kg is about to be pushed on a floor of coefficient of friction 0.3. The magnitude of the force of friction on the wooden block when it is just pushed is $\left( {g = 10\,m/{s^2}} \right).$

Assertion: When a person walks on a rough surface, the frictional force exerted by the surface on the person is opposite to the direction of the tendency of motion of his legs.
Reason: If a body moves with constant velocity, it implies that it is moving along a straight line and there is no acceleration.

A brick of mass 3 kg just begins to side down on inclined plane at an angle of $60^\circ$ with the horizontal. The force of friction will be

A block of mass 1 kg slides down on a rough inclined plane of inclination 60° starting from its top. If the coefficient of kinetic friction is 0.5 and length of the plane is 1 m, then work done against friction is (Take $g = 9.8\;m/{s^2}$)