Q: A car covers the first half of a distance at 30 km/h and the second half at 60 km/h. Its average speed for the whole journey is:

40 km/h. For equal distances, average speed = \dfrac{2 \times 30 \times 60}{30 + 60} = 40 km/h (45 km/h wrongly averages the speeds).

Q: A body moving at 10 m/s accelerates uniformly at 2 m/s². The distance it covers in the next 3 s is:

39 m. s = ut + \tfrac12 a t^2 = (10)(3) + \tfrac12 (2)(9) = 30 + 9 = 39 m.

Question 1

Two forces of 3 N and 4 N act on a body at right angles to each other. The magnitude of their resultant is:

Accepted Answer

5 N. For perpendicular vectors the resultant = \sqrt{3^2 + 4^2} = \sqrt{25} = 5 N (not the scalar sum 7 N).

Question 2

A boy walks 6 m towards the east and then 8 m towards the north. The magnitude of his net displacement is:

Accepted Answer

10 m. Perpendicular displacements add as vectors: \sqrt{6^2 + 8^2} = \sqrt{100} = 10 m (14 m is the total distance).

Question 3

An athlete completes exactly one full round of a circular track of radius 7 m. His displacement is:

Accepted Answer

0 m. After one complete round he returns to the start, so displacement is 0 (the distance covered is 2\pi r = 44 m).

Question 4

A runner covers half a round of a circular track of diameter 14 m. His displacement is (take \pi = 22/7):

Accepted Answer

14 m. Half a round ends at the diametrically opposite point, so displacement = diameter = 14 m (distance = \pi r = 22 m).

Question 5

A car covers the first half of a distance at 30 km/h and the second half at 60 km/h. Its average speed for the whole journey is:

Accepted Answer

40 km/h. For equal distances, average speed = \dfrac{2 	imes 30 	imes 60}{30 + 60} = 40 km/h (45 km/h wrongly averages the speeds).

Question 6

A body can have a constant speed but a changing velocity when it moves:

Accepted Answer

in a circular path at a steady rate. In uniform circular motion the direction changes continuously, so velocity changes even though the speed is constant.

Question 7

A car moving at 90 km/h is brought to rest in 5 s. Its retardation is:

Accepted Answer

5 m/s². Convert: 90 km/h = 25 m/s; retardation = \dfrac{25}{5} = 5 m/s² (18 m/s² comes from forgetting to convert km/h).

Question 8

Assertion (A): A body thrown vertically upward has zero velocity but non-zero acceleration at its highest point. Reason (R): At the highest point gravity still acts on the body.

Accepted Answer

Both A and R are true and R is the correct explanation of A. At the top v = 0, but gravity (g) still acts downward, so acceleration is non-zero — R correctly explains A.

Question 9

On a velocity–time graph, a straight line rises from 0 to 20 m/s in 4 s. The acceleration represented is:

Accepted Answer

5 m/s². On a v–t graph, acceleration = slope = \dfrac{20 - 0}{4} = 5 m/s².

Question 10

A body moving at 10 m/s accelerates uniformly at 2 m/s². The distance it covers in the next 3 s is:

Accepted Answer

39 m. s = ut + 	frac12 a t^2 = (10)(3) + 	frac12 (2)(9) = 30 + 9 = 39 m.

Question 11

A car moving at 20 m/s applies brakes producing a retardation of 5 m/s². The distance it travels before stopping is:

Accepted Answer

40 m. v^2 = u^2 - 2as \Rightarrow 0 = 400 - 2(5)s \Rightarrow s = \dfrac{400}{10} = 40 m.

Question 12

The stopping distance of a vehicle (for the same braking force) is proportional to the square of its speed. If the speed is doubled, the stopping distance becomes:

Accepted Answer

4 times. Since s \propto v^2, doubling v multiplies the stopping distance by 2^2 = 4.

Question 13

Which of the following groups contains ONLY vector quantities?

Accepted Answer

Displacement, velocity, acceleration, force. Vectors need magnitude AND direction: displacement, velocity, acceleration and force qualify; distance, speed, mass, time and energy are scalars.

Question 14

Assertion (A): The distance covered by a body can never be negative. Reason (R): Distance is a scalar quantity that only has magnitude.

Accepted Answer

Both A and R are true and R is the correct explanation of A. Distance is a scalar (magnitude only), so it is always positive or zero — R correctly explains A.

Question 15

A quantity that depends only on the initial and final positions of a body, and not on the path taken, is:

Accepted Answer

Displacement. Displacement is the straight line from start to finish; it is path-independent, unlike distance.

Question 16

Which one of the following is a scalar quantity?

Accepted Answer

Speed. Speed has magnitude only, so it is a scalar; velocity, displacement and acceleration are vectors.

Question 17

A body moves 4 m towards the north and then 3 m towards the east. The distance and displacement respectively are:

Accepted Answer

7 m and 5 m. Distance = 4 + 3 = 7 m; displacement = \sqrt{4^2 + 3^2} = 5 m.

Question 18

A car travels 5 km due east and then returns 5 km due west to its starting point. Its total distance and displacement are:

Accepted Answer

10 km and 0 km. Distance is the whole path = 10 km; since it returns to start, displacement = 0.

Question 19

The magnitude of displacement is equal to the distance travelled only when the body moves:

Accepted Answer

along a straight line without changing direction. Only in straight-line motion without reversing does the path length equal the straight-line displacement.

Question 20

Assertion (A): The displacement of a moving body can be zero even when the distance covered is not zero. Reason (R): Displacement is the shortest distance between the initial and final positions.

Accepted Answer

Both A and R are true and R is the correct explanation of A. If a body returns to its start, displacement is zero though distance is not — because displacement is the shortest (straight-line) separation, which R correctly explains.

Motion & Kinematics — Homi Bhabha Exam Physics MCQs with Solutions

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