A helicopter of mass 1000 kg reises with a vertical acceleration of 15m /s². The crew and the passengers weigh 300 kg. Give the magnitude and direction of the force on the helicopter due to the surrounding air, take g = 10 m/s².

A stone of mass 0.25 kg tied to the end of a string is whirled round in a circle of radius 1.5 m with a speed of 40 rev./min in a horizontal plane. What is the tension in the string ? What is the maximum speed with which the stone can be whirled around if the string can withstand a maximum tension of 200 N ?

An aircraft executes a horizontal loop at a speed of 720km/h with its wings banked at 15^o . What is the radius of the loop?

Ten one-rupee coins are put on top of each other on a table. Each coin has mass m. Give the magnitude and direction of  the reaction of the 6th coin on the 7th coin.(counted from the bottom)

A light, inextensible string connects two blocks of mass M₁, and M₂. A force Facts upon M_I. Find acceleration of the system and tension in siring.

Is a 'single isolated force' possible in nature?

A force of 400 N acting horizontal pushes up a 20 kg block placed 'On a rough inclined plane which makes an angle of 45° with the horizontal. The acceleration experienced by the block is 0.6 m/s², Find the coefficient of sliding friction between the box and incline.

The driver of a truck travelling with a velocity v suddenly notices a brick wall in front of him at a distance d. Is it better for him to apply brakes or to make a circular turn without applying brakes in order to just avoid crashing into the wall? Why?

A body m₁ of mass 9 kg and another body m₂ of mass 6 kg are connected by a light inextensible string, Consider a smooth inclined plane of inclination 30° over which one of them can be placed while the other hangs vertically and freely, Show that m₁ will drag m₂ up the whole length of the plane in half the time that m₂ hanging vertically would take to draw m₁ up the plane.

An object weighing 70 kg is kept in a lift. Find its weight as recorded by a spring balance when the lift
(a) moves upwards with a uniform velocity of 5 ms^-1,
(b) moves upwards with a uniform acceleration of 2.2 ms^-2,
(c) moves downwards with a uniform acceleration of 2.8 ms^-2 and
(d) falls freely under gravity.

Give one argument in favour of the fact that frictional force is a non-conservative force.

A cricket ball of mass 150 g is moving with a velocity of 12 ms^-1 and is hit by a bat so that the ball is turned back with a velocity of 20 ms^-1. The force of the blow acts for 0.01 s. Find the average force exerted on the ball by the bat.

A trolley of mass 20 kg rests on a horizontal surface. A massless string tied to the trolley passes over a frictionless pulley and a load of 5 kg is suspended from other end of string. If coefficient of kinetic friction between trolley and surface be 0.1, find the acceleration of trolley and tension in the string. (Take g = 10 m S^-2)

In the system of three blocks A, Band C shown in figure, (i) how large a force F is needed to give the blocks an acceleration of 3 m/s², if the coefficient of friction between blocks and table is 0.27 (ii) how large a force does the block A exert on the block B?

Vipul was driving on the road with his old Grandmother. She was sitting on the front seat with him. When Vipul was about to reach his destination, he stopped the engine and did not apply the brakes. Even then the car was running on the road for sometimes. His grandmother surprised and asked her grandson the reason of the car running without the engine on. Vipul was the student of Science studying is class XI. He explained his grandmother that it is only the momentum due to which the car is going on:
(i) What values Vipul exhibit here?
(ii) What is momentum and on which factors it depends?