Exploring Forces

A force is BEST described as:

1. aA type of energy
2. bA push or pull on an object
3. cA property of mass alone
4. dAlways a contact phenomenon

Which of the following is a NON-CONTACT force?

1. aFriction
2. bTension in a rope
3. cPush given by hand
4. dGravitational force

Which of the following effects can a force NOT produce on its own?

1. aChange the speed of an object
2. bChange the colour of an object
3. cChange the shape of an object
4. dChange the direction of motion of an object

Two equal and opposite forces act on a stationary box on a smooth floor. The box will:

1. aMove in the direction of the larger force
2. bMove in the direction of the smaller force
3. cRemain at rest because the two forces balance each other
4. dOscillate to and fro

The SI unit of force is the:

1. aJoule
2. bNewton
3. cPascal
4. dWatt

When a ball is rolled on a rough floor it slows down and finally stops. The MAIN cause is:

1. aAir pushing the ball
2. bGravity pulling the ball backwards
3. cFriction between the ball and the floor opposing motion
4. dLoss of mass of the ball

1. I. Muscular force is a contact force.
2. II. Friction can act between two objects even when they are not touching each other.
3. III. A magnet can exert a force on an iron nail without touching it.

Which of the statements above about contact and non-contact forces is/are correct?

1. aOnly I and III
2. bOnly II and III
3. cI, II and III
4. dOnly I and II

Assertion (A): When you push a table with your hand, your hand also experiences a force.

Reason (R): A force can act between two objects only when they are in contact with each other.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

On a spring balance, the bigger marks are at 0 N, 2 N, 4 N and so on, and the gap between two bigger marks is divided into 4 equal small divisions. The smallest weight this spring balance can read is:

1. a0.25 N
2. b2 N
3. c8 N
4. d0.5 N

Friction is sometimes called a ‘double-edged sword’ because it:

1. aHelps us in walking, gripping and braking but also wastes energy as heat in machines
2. bLooks like a sword
3. cAlways increases speed of motion
4. dHas no useful purpose

In which of the following actions does the applied force mainly change the SHAPE of an object rather than its motion?

1. aKicking a football lying on the ground
2. bA fielder stopping a moving ball
3. cRolling a chapati with a rolling pin
4. dTurning the steering handle of an autorickshaw

Match List I with List II:

1. a(i)-P, (ii)-Q, (iii)-R, (iv)-S
2. b(i)-Q, (ii)-P, (iii)-R, (iv)-S
3. c(i)-R, (ii)-P, (iii)-S, (iv)-Q
4. d(i)-Q, (ii)-P, (iii)-S, (iv)-R

1. I. Two balloons rubbed with the same woollen cloth repel each other.
2. II. A balloon rubbed with a woollen cloth and that cloth attract each other.
3. III. When a balloon is rubbed with a woollen cloth, only the balloon gets charged.

Which of the statements above about charged balloons is/are correct?

1. aOnly I
2. bOnly I and II
3. cOnly II and III
4. dI, II and III

Assertion (A): When a ball is thrown up, friction with air acts downward.

Reason (R): Friction always acts opposite to the direction of relative motion (or attempted motion).

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

A stone weighing 5 N is fully immersed in water. The water it displaces weighs 2 N. According to Archimedes’ Principle, the stone will:

1. aSink, because the weight of the water it displaces is less than its own weight
2. bFloat, because the buoyant force on it is larger than its weight
3. cStay at any depth, because the two forces on it are equal
4. dFloat, because water applies an upward force on it

The mass of an object is a measure of:

1. aThe pull of gravity on it
2. bThe amount of matter contained in it
3. cIts surface area
4. dIts temperature

Which of the following statements is CORRECT for a body taken from the Earth to the Moon?

1. aBoth mass and weight increase
2. bMass decreases; weight remains the same
3. cMass remains the same; weight decreases
4. dBoth mass and weight decrease equally

A boy pushes a heavy crate but it does not move at all. Which statement is TRUE?

1. aThe boy applied no force at all
2. bThe crate is glued to the floor
3. cFriction has the wrong direction
4. dThe boy’s push is balanced by the force of friction from the floor

Two ring magnets are slipped onto a vertical wooden stick with like poles facing each other, so the upper magnet floats above the lower one. Both magnets are taken off, each is turned upside down, and they are put back on the stick in the same order. The upper magnet will now:

1. aStill float, because turning a magnet upside down removes its magnetism
2. bFall onto the lower magnet, because the facing poles are now unlike poles
3. cFall onto the lower magnet, because a magnet cannot exert a force without touching
4. dStill float, because the facing poles are again like poles and repel each other

Assertion (A): An object dropped near the Earth gains speed as it falls.

Reason (R): On a freely falling object, the only force acting (in the absence of air resistance) is the force of gravity.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

Aeroplanes, ships and high-speed trains are given specially designed shapes. The main reason is to:

1. aReduce the force of friction exerted by the air or water around them
2. bMake them heavier so that they move steadily
3. cIncrease the upthrust of the air on them
4. dIncrease the gravitational pull of the Earth on them

1. I. Objects of different weights stretch the same spring by different amounts.
2. II. Gravitational force can be attractive as well as repulsive.
3. III. The force with which the Earth pulls an object towards itself is called its weight.

Which of the statements above about gravitational force and weight is/are correct?

1. aOnly I and II
2. bOnly I and III
3. cOnly II and III
4. dI, II and III

Why are the soles of athletic shoes given a deep zig-zag pattern?

1. aTo make them look fashionable
2. bTo make them lighter
3. cTo increase friction with the ground for better grip
4. dTo reduce friction with the ground

Engineers used to think a perfectly polished, mirror-smooth surface would have ZERO friction. In practice this is NOT true because:

1. aThe surface is too soft
2. bPolishing makes a surface heavier
3. cEven surfaces that look smooth have a large number of minute irregularities that lock into each other
4. dMirror surfaces always reflect light

Buoyant force is BEST described as:

1. aThe downward pull of gravity
2. bA push exerted upward by a fluid on an object placed in it
3. cA type of friction
4. dA force exerted only by solids

Assertion (A): A rock can never float on water.

Reason (R): Pumice, a rock formed during volcanic eruptions, is full of tiny air pockets and is less dense than water.

1. aBoth A and R are true, and R is the correct explanation for A
2. bBoth A and R are true, but R is NOT the correct explanation for A
3. cA is true, but R is false
4. dA is false, but R is true

In the friends’ experiment, the spring balance reading is largest with sandpaper and smallest with polished plastic. The variable being studied here is the:

1. aRoughness of the surface in contact (between block and floor)
2. bMass of the block
3. cLength of the spring balance
4. dVolume of the block

Which of the following changes in the experiment would be MOST likely to give a fair comparison of friction across the four wrappings?

1. aUse a different mass for each wrapping
2. bPull at different speeds for each trial
3. cUse a heavier spring balance
4. dUse the SAME block on the SAME tile floor each time, change only the wrapping

If the friends now repeat the experiment but pour a thin film of oil on the tile floor before pulling each block, the readings will MOST likely:

1. aStay exactly the same
2. bAll become larger because the oil makes the floor stickier
3. cAll become smaller because the oil reduces friction with every wrapping
4. dShow that sandpaper is now the smoothest

From their data the friends conclude: ‘The smoother the contact, the smaller the friction.’ This conclusion is BEST described as:

1. aA reasonable generalisation supported by their experiment within its tested conditions
2. bA fact that holds for every situation in the universe
3. cAn opinion only
4. dA theorem in mathematics