Laws of motion practice · Medium

To the free end of spring hanging from a rigid support, a block of mass m is hung and slowly allowed to come to its equilibrium position. Then stretching in the spring is d. if the same block is attached to the same spring and allowed to fall suddenly, the amount of stretching is (force constant ,k)

A student unable to answer a question on Newton’s law of motion attempts to pull himself up by tugging on his hair. He will not succeed

One feels heavier in a lift when the lift

When a bus of mass $1000 \mathrm{~kg}$ is moving with a velocity of $20 \mathrm{~ms}^{-1}$ on a rough horizontal road, surface its engine is switched off then, how far does the bus move before it comes to rest (velocity $=0$ ) if the coefficient of kinetic friction between the road surface and tyres of the bus is 0.75 ?

A box of mass m kg is placed on the rear side of an open truck accelerating at $t\;\mathrm{m}{\mathrm{s}^{ - 2}}$. The coefficient of friction between the box and the surface below it is 0.4. The net acceleration of the box with respect to the truck is zero. The value of m is [Given $\mathrm{g} = 10\mathrm{\;m}{\mathrm{s}^{ - 2}}$)

A golf ball of mass $50 \,{gm}$ placed on a tee, is truck by a golf-club. The speed of the golf ball as it leaves the tee is $100 {~m} / {s}$, the time of contact on the ball is $0.02 {~s}$. If the force decreases to zero linearly with time, then the force at the beginning of the contact is

A lift is moving upwards with a uniform velocity v in which a block of mass m is lying. The frictional force offered by the block, when coefficient of the frictional is $\mu$, will be

Assertion : A cyclist always bends inwards while negotiating a curve.
Reason : By bending, cyclist lowers his centre of gravity.

When a particle moves in a circle with a uniform speed

Assertion: Animate object can accelerate in the absence of external force.

Reason: Newton's second law is not applicable on animate object.

A motorcyclist wants to drive on the vertical surface of wooden 'well' of radius $5 \mathrm{~m}$, with a minimum speed of $5 \sqrt{5} \mathrm{~ms}^{-1}$. The minimum value of coefficient of friction between the tyres and the wall of the well must be (Take, $g=10 \mathrm{~ms}^{-2}$)

A car moves at a speed of $20 \mathrm{~ms}^{-1}$ on a banked track and describes an arc of a circle of radius $40 \sqrt{3} \mathrm{~m}$. The angle of banking is $\left(\mathrm{g}=10 \mathrm{~ms}^{-2}\right)$

A lift of mass $1000 \mathrm{~kg}$ which is moving with acceleration of $1 \mathrm{~m} / \mathrm{s}^2$ in upward direction, then the tension developed in string which is connected to lift is

A block is lying on the horizontal frictionless surface. One end of a uniform rope is fixed to the block which is pulled in the horizontal direction by applying a force $F$ at the other end. If the mass of the rope is half the mass of the block, the tension in the middle of the rope will be

Assertion: A man in a closed cabin falling freely experience weightlessness.
Reason: Inertial and gravitational mass have equivalence.

A parachutist is in free fall before opening her parachute. The net force on her has a magnitude $F$ and is directed downwards. This net force is somewhat less than, her weight $w$ because of air resistance. Then, she opens her parachute. At the instant after her parachute fully inflates, the net force on her would be

Which of the following statement is NOT true for kinetic friction?

Statement-1: A man starts walking towards west. Friction force on him acts towards east.
Statement-2 : Friction opposes relative motion.

A shell initially at rest explodes into two pieces of equal mass, then the two pieces will

A body of weight 64 N is pushed with just enough force to start it moving across a horizontal floor and the same force continues to act afterwards. If the coefficients of static and dynamic friction are 0.6 and 0.4 respectively, the acceleration of the body will be (Acceleration due to gravity =g)

Statement-I: The apparent weight of a body in an elevator moving with some downward acceleration is less than the actual weight of body.
Statement-II: The part of the weight is spent in producing downward acceleration, when body is in elevator.

Statement-I: When the lift moves with uniform velocity the man in the lift will feel weightlessness.
Statement-II: In downward accelerated motion of lift, apparent weight of a body increases.

Shock absorbers are used in vehicles to reduce the magnitude of

Assertion : Impulse of force and momentum are same physical quantities.
Reason : Both quantities have same unit.

It is easier to draw up a wooden block along an inclined plane than to haul it vertically, principally because

The position vector of a particle related to time $t$ is given by $\vec{r}=\left(5 t^2 \hat{i}+3 t \hat{j}+4 \hat{k}\right)$. The direction of net force experienced by the particle is

A block can slide on a smooth inclined plane of inclination $\mathrm{\theta }$ kept on the floor of a lift. When the lift is descending with a retardation a, the acceleration of the block relative to the incline is

A body takes time t to reach the bottom of an inclined plane of angle $\theta$ with the horizontal. If the plane is made rough, time taken now is 2t. The coefficient of the friction of the rough surface is

A ball moves in a frictionless inclined table without slipping. The work done by the table surface on the ball is

A body of mass $0.1 {~kg}$ attains a velocity of ${1 0}$ ${ms}^{-1}$ in $0.1 {~s}$. The force acting on the body is