Laws of motion practice · Mixed difficulty

A spring balance and a physical balance are kept in a lift. In these balances equal masses are placed. If now the lift starts moving upwards with constant acceleration, then

A lift is descending with a constant velocity ' ${v}$ '. A man in the lift drops a coin. The coin experiences an acceleration towards the floor equal to :

Formula for true force is

Assertion: Frictional force opposes relative motion and dissipates power in the form of heat.
Reason: Friction is always an undesirable force.

When an elevator cabin falls down, the cabin and all the bodies fixed in the cabin are accelerated with respect to

If a stone is thrown out of an accelerated train, then
acceleration of the stone at any instant depends on

Statement I: A cloth covers a table. Some dishes are kept on it. The cloth can be pulled out without dislodging the dishes from the table.
Statement II: For every action there is an equal and opposite reaction.

A platform is moving upwards with an acceleration of $5 \mathrm{~ms}^{-2}$. At the moment when its velocity is $u=3 \mathrm{~ms}^{-1}$, a ball is thrown from it with a speed of $30 \mathrm{~ms}^{-1}$ w.r.t. platform at an angle of $\theta=30^{\circ}$ with horizontal. The time taken by the ball to return to the platform is

Choose the wrong statement

Statement I: If bodies slide down an inclined plane without rolling, then all the bodies reach the bottom simultaneously.

Statement II: Acceleration of all bodies are equal and independent of shape.

A body of mass $10 {~kg}$ is acted upon by a force given by equation $F=\left(3 t^2-30\right)$ Newton's, The initial velocity of the body is $10 {~m} / {s}$. The velocity of the body after $5 {sec}$ is

A spacecraft of mass M is moving with velocity v in free space when it explodes and breaks in two. After the explosion, a mass m of the spacecraft is left stationary. What is the velocity of other part?

External agencies like gravitational and magnetic forces ...X...
exerts force on a body from a distance.
Here, X refers to

The net force acting is not zero on

The velocity of a body of mass $20\,kg$ decreases from $20\,m/s$ to $5\,m/s$ in a distance of $100\,\,\,m$ Force on the body is

An athlete does not come to rest immediately after crossing the winning line due to the

Which of the following statement (s) is/are incorrect?

Two equals forces are acting at a point with an angle of $60^{\circ}$ between them. If the resultant force is equal to $40 \sqrt{3} \mathrm{~N}$, the magnitude of each force is

A body of mass $m$ is launched up on a rough inclined plane making an angle $45^{\circ}$ with horizontal. If the time of ascent is half of the time of descent, the frictional coefficient between plane and body is

Statement-I: Newton's third law of motion is applicable only when bodies are in motion or rest.
Statement-II: Newton's third law applies to all types of force, e.g. gravitational, electric or magnetic forces etc.

Assertion: When a force $\vec{F}$ attempts to slide a body along a surface, a frictional force parallel to the surface and directed so as to oppose the sliding, is exerted on the body by the surface.
Reason: It is due to the bonding between the body and the surface.

Assertion : The two bodies of masses M and m (M > m) are allowed to fall from the same height if the air resistance for each be the same then both the bodies will reach the earth simultaneously.
Reason : For same air resistance, acceleration of both the bodies will be same.

A body of mass 10 kg is projected from the ground with a velocity 30 m/s at an angle $60^\circ$ with the vertical. If ${t_1}$ is the time in seconds at which the body is projected and ${t_2}$ is the time in seconds at which reaches the ground. The change in momentum in $kgm{s^{ - 1}}$ during the time $\left( {{t_2} - {t_1}} \right)$ is

Statement-I: A concept of pseudo forces is valid both for inertial as well as non-inertial frame of reference
Statement-II: A frame accelerated with respect to an inertial frame is a non-inertial frame.

A lift of mass $2000 \mathrm{~kg}$ is supported by thick steel ropes. If maximum upward acceleration of the lift be $1.2 \mathrm{~ms}^{-2}$, and the breaking stress for the ropes be $2.8 \times 10^8 \mathrm{~Nm}^{-2}$, what should be the minimum diameter of rope?

Statement-I: If the force varies with time in a complicated way then the net force is measured by the total change in momentum of the body.
Statement-II: Change in momentum and impulsive force are numerically equal.

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?

In the above ques., the height to which the lift takes the passenger is

A particle of mass $m$ is moving with a uniform velocity $v_1$. It is given an impulse such that its velocity becomes $v_2$. The impulse is equal to