Motion and Force

Statement (1) is wrong. Tyres and soles of shoes have geometrical patterns to increase the friction.
Statement (2) is correct. The straps of the shoulder bags are made broad to decrease the pressure by increasing the area of contact.
Statement (3) is correct. Aeroplanes and boats have streamlined shapes to reduce the resistance offered by air and water, respectively.

(1) Statement (1) is wrong. When a person is standing on a weighing scale in a lift, which is moving upwards, the weighing scale shows more weight.
(2) Statement (2) is wrong. The weight of an object would be minimum, when it is placed at the centre of earth because it experiences gravitational pull from all the sides. Thus, the net weight of an object remains to be zero.
(3) Statement (3) is wrong. Mass is a measure of the quantity of matter, whereas weight is a measure of force.

Statement (1) is wrong. When a truck is fully loaded, its centre of gravity will be raised making it unstable. When taking a sharp turn the vertical line through the centre of gravity will fall outside the base of support, and the truck may topple over.
Statement (2) is also incorrect. While throwing a ball upwards, the acceleration remains the constant.

(1) Statement (1) is correct. When a coolie goes upstairs with a load on his head, work is done against the force of gravity.
(2) Statement (2) is wrong. A vehicle moving on a circular path experiences centripetal force.
(3) Statement (3) is wrong. If a boy sitting in a railway train, moving at constant velocity, throws a ball straight up into the air, the ball will fall into his hand.

(i) Statement (1) is correct. Body will weigh more in vacuum as there is no up thrust in vacuum. In air, the air column offers an up thrust and so there is an apparent loss of weight when weighed in air.
(ii) Statement (2) is correct. When a barometer is taken to a mine the pressure increases. In a mine, the gases present are denser so the pressure is more. Hence, the height of mercury column increases.

The boy will not feel any change in weight of the ply wood. According to Newton's law of motion, action and reaction will be equal to each other.
The action done by the feet of the bird will be equal to reaction produced by wooden ply. So, the ply shows no change in weight.

Statement (1) is wrong. If the beaker moves with a vertical acceleration, the wooden plank will remain in the same position relative to the water.

Statement (1) is wrong. If a small part separates from an orbiting satellite, the part will continue to move in the same orbit as the satellite due to centrifugal force.

(1) Statement (1) is wrong. If the distance between sun and the earth is doubled, the gravitational force between them will become one-fourth.
(2) Statement (2) is also wrong. Carpenters use the sand paper to polish the wood by increasing the force of friction.

1. A body floats if its density is lesser than the density of the liquid.
   Density of egg is greater than density of pure water. So, it remains at the bottom. But when salt is added the density of salt water becomes more than density of egg. So, the egg rises and floats.
2. The outer layer of egg is impermeable to water.

Statement (1) is wrong. An athlete made to fall on a cushioned bed or on a sand bag to increase the time of the athlete's fall to stop after making the jump. This decreases the rate of change of momentum and hence the force.
Statement (2) is correct. The base of the tower is larger than the rest of the tower. Hence the centre of gravity falls within the base of support.

(1) While scuba diving, the person notices air bubbles underwater. The size of a bubble is small when it is deep underwater. But the size increases as it moves upwards.
(2) It is due to decrease in pressure applied by water column on air bubbles as they rise up.

Statement (1) is wrong. When a body is in circular motion, no work is said to be done by centripetal force.
Statement (2) is wrong. The hand flour grinder is provided with a handle near its rim, because the perpendicular distance of the line of action of the force from the axis of rotation will be maximum to get the largest turning effect.

Statement (1) is incorrect. In case of uniform circular motion, the acceleration is constant in magnitude and directed radial inwards.
Statement (2) is also incorrect. The force applied as push, pull, stretch and squeeze is called muscular force.

Statement (1) is correct. The gravitational force with which the earth attracts the moon is equal to the force with which the moon attracts the earth. If it is decreased, the earth attracts the moon.
Statement (2) is wrong. The weight of a body at the centre of Earth is zero, due to lack of gravitational force.