CBSE Class 6 Science Advanced Physics Motion and Measurement of Distances MCQs Set 02

Answer: (c) 10 km

Explanation:
1. Time = 10 min = 10/60 h = 1/6 h.
2. Distance = speed × time = 60 × 1/6 = 10 km.

Teacher's Note:
1. Change minutes to hours when the speed is in km/h.
2. Distance = speed × time.

Answer: (a) 10000 metres

Explanation:
1. 1 km = 1000 m.
2. Only 10000 m is greater than 1000 m, so a kilometre is smaller than 10000 metres.
3. 995 m and 990 m are smaller, and 1000 m is equal.

Teacher's Note:
1. Compare after converting to the same unit.
2. 'Lesser' means strictly smaller, not equal.

Answer: (c) rotational motion

Explanation:
1. The blades spin about a fixed axis.
2. Spinning about an axis is rotational motion.

Teacher's Note:
1. Fans, tops, wheels and blades rotate.
2. Compare with oscillation, which is to-and-fro.

Answer: (d) A simple pendulum is used to measure the mass of a bob.

Explanation:
1. Delhi to Hyderabad is more than a thousand kilometres, so km is the right unit; (a) is true.
2. 100 cm = 1 m, so (b) is true.
3. 1 tonne = 1000 kg = 1000 × 1000 g = 10⁶ g, so (c) is true.
4. A simple pendulum is used to measure time (it is the basis of pendulum clocks), not mass. So (d) is the incorrect statement.

Teacher's Note:
1. A mass is measured with a balance.
2. 1 tonne = 10⁶ g is a handy fact to remember.

Answer: (a) The motion of a swing is rectilinear as well as circular.

Explanation:
1. A swing moves to and fro along a curved arc, so its motion is oscillatory, not rectilinear and circular.
2. A guitar string vibrates, a clock pendulum oscillates and a fan rotates, so (b), (c) and (d) are true.
3. The false statement is (a).

Teacher's Note:
1. Name a motion by its pattern, not by words in the options.
2. To-and-fro means oscillatory.

Answer: (b) (i) & (ii)

Explanation:
1. The drill bit spins about its axis, which is rotatory motion (i).
2. It also moves forward into the wood along a straight line, which is translatory motion (ii).
3. So the correct pair is (i) and (ii).

Teacher's Note:
1. A motion with two kinds together is called combined motion.
2. A screw going into wood is another example.

Answer: (b) 2 and 3 only

Explanation:
1. When two hard metal balls collide, each ball pushes the other back.
2. Their speeds change and the directions of motion change as well.
3. Hard metal balls do not change shape or volume noticeably, so the answer is 2 and 3 only.

Teacher's Note:
1. A collision changes the state of motion of the bodies.
2. Think about a billiard ball hitting another.

Answer: (c) t = T/4

Explanation:
1. R is the middle (mean) position and P and Q are the two extreme positions.
2. One full oscillation is R → Q → R → P → R, which takes time T.
3. The trip from R to Q is one quarter of this, so t = T/4.

Teacher's Note:
1. Split the full swing into four equal parts.
2. Mean to extreme takes one quarter of the time period.

Answer: (a) Rotatory motion

Explanation:
1. The disk and the stick spin about an axis through the centre.
2. The stick turns about its own axis without moving away, which is rotatory motion.

Teacher's Note:
1. Spinning about its own axis is rotation.
2. Circular motion is the motion of a point going round a centre, such as a clock tip.

Answer: (b) It will keep moving between point A and B and will never stop.

Explanation:
1. Gravity pulls the ball down to C, where it has the most speed.
2. With no friction there is no loss of energy, so it climbs the other side to the same height as A.
3. It will then return, so it keeps moving between A and B and never stops.

Teacher's Note:
1. Friction is what slows and stops a rolling ball.
2. Without friction the ball reaches B and not beyond it.

Answer: (c) Rotational and linear

Explanation:
1. The ball spins about its own centre, which is rotational motion.
2. At the same time it moves down the slope along a straight line, which is linear motion.
3. So it has rotational and linear motion together.

Teacher's Note:
1. A rolling ball always has two motions: spinning and moving forward.
2. The ball does not repeat its path, so its motion is not periodic.

Answer: (b) a-4, b-1, c-2, d-3

Explanation:
1. A rupee coin is very small, so its area is measured in cm² (a-4).
2. A cricket field is a few thousand square metres, so m² (b-1).
3. A paddy field is large and is measured in hectares (c-2).
4. A country is huge and is measured in km² (d-3).
5. This matches option (b).

Teacher's Note:
1. Choose a unit that gives a number of a handy size.
2. 1 hectare = 10,000 m².

Answer: (b) The displacement is zero

Explanation:
1. In one hour the minute hand makes one full turn and its tip comes back to where it started.
2. The straight-line change in position (displacement) is therefore zero.
3. The distance covered is the length of the circle, which is not zero, so the average speed is not zero either.

Teacher's Note:
1. Distance is the path length; displacement is the change of position.
2. After a full circle the tip is back at the start.

Answer: (a) P

Explanation:
1. The time period of a simple pendulum increases as its length increases.
2. Pendulum P has the longest string.
3. So P has the longest time period.

Teacher's Note:
1. Longer pendulum, slower swing.
2. Compare the string lengths, not the size of the bobs.

Answer: (b) (a)-(ii) (b)-(i) (c)-(iv) (d)-(iii)

Explanation:
1. 300 mm = 300 ÷ 10 = 30 cm, so (a)-(ii).
2. 300 cm = 3 m, so (b)-(i).
3. 300 m = 300 × 100 = 30000 cm, so (c)-(iv).
4. 300 km = 300 × 1000 = 300000 m, so (d)-(iii).
5. This is option (b).

Teacher's Note:
1. Convert each one separately and tick it off.
2. Going to a smaller unit multiplies; going to a larger unit divides.

Answer: (b) (ii) and (iii)

Explanation:
1. (i) 10 cm = 1 dm is correct.
2. (ii) 20 m = 0.02 km, not 2000 km, so it is incorrect.
3. (iii) 30 mm = 3 cm, not 30000 cm, so it is incorrect.
4. (iv) 40 m = 40 × 10 dm = 400 dm is correct.
5. The incorrect pairs are (ii) and (iii), option (b).

Teacher's Note:
1. Check every pair and mark the wrong ones.
2. A big number for a bigger unit is a sign of a mistake.

Answer: (c) (a) (i), (ii); (b) (i), (ii); (c) (ii), (iii)

Explanation:
1. (a) The earth goes round the sun along a closed path again and again: circular (i) and periodic (ii).
2. (b) The hands of a clock go round and repeat: circular (i) and periodic (ii).
3. (c) A pendulum swings to and fro and repeats: periodic (ii) and oscillatory (iii).
4. This matches option (c).

Teacher's Note:
1. A single object can fit more than one description.
2. Both circular and oscillatory motions are kinds of periodic motion.

Answer: (c) Y

Explanation:
1. With no loss of energy the bob rises on the other side to exactly the same height from which it started.
2. B is level with Y in the figure, while W is the lowest point, X is lower than B and Z is higher than B.
3. So the bob will stop for a moment at Y.

Teacher's Note:
1. At the highest point of a swing the bob stops for an instant.
2. Equal height on both sides is the key idea.

Answer: (c) Its inertia

Explanation:
1. The property of a body by which it resists any change in its state of rest or of motion is called inertia.
2. Speed, acceleration and weight do not describe this property.

Teacher's Note:
1. A passenger jerks forward when a bus brakes because of inertia.
2. More mass means more inertia.

Answer: (b) (i) - (c), (ii) - (a), (iii) - (d), (iv) - (b)

Explanation:
1. (i) A body moving along a curved track has curvilinear motion, (c).
2. (ii) An apple falling from the tree falls along a straight line, rectilinear motion, (a).
3. (iii) A spinning top turns about its own axis, rotatory motion, (d).
4. (iv) A swinging cradle or swing moves to and fro, oscillatory motion, (b).
5. The pairs are (i)-(c), (ii)-(a), (iii)-(d), (iv)-(b).

Teacher's Note:
1. Name the path first: curved, straight, spinning or to-and-fro.
2. The pictures are shown as simple sketches here.