All Free Physics MCQs with Answers

1. What is the SI unit of force?

• A. Joule
• B. Watt
• C. Newton
• D. Pascal

Explanation: The SI unit of force is the newton (N), defined as the force that accelerates a one-kilogram mass at one metre per second squared. The joule is the unit of energy, the watt of power and the pascal of pressure.

2. What is the approximate speed of light in a vacuum?

• A. 3 × 10⁶ m/s
• B. 3 × 10⁸ m/s
• C. 3 × 10¹⁰ m/s
• D. 3 × 10⁵ m/s

Explanation: Light travels at approximately 3 × 10⁸ metres per second in a vacuum — about 300,000 kilometres per second. This is the maximum speed at which any information can travel, and light slows down in denser media such as glass or water.

3. Newton's second law of motion is most generally stated as

• A. force equals mass times velocity
• B. force equals the rate of change of momentum
• C. force equals mass times distance
• D. force equals momentum times time

Explanation: The general statement is that the net force equals the rate of change of momentum, which reduces to F equal to ma only when the mass is constant. The general form is needed for a rocket, whose mass falls as fuel burns. Mass times velocity is momentum itself, not force.

4. A body moving with uniform velocity has

• A. a net force acting on it in the direction of motion
• B. zero net force acting on it
• C. a net force acting opposite to its motion
• D. an increasing acceleration

Explanation: Uniform velocity means zero acceleration, and by Newton's second law zero acceleration requires zero net force. The individual forces need not be absent: a car at steady speed has thrust and friction that cancel exactly. A non-zero net force would necessarily change either the speed or the direction.

5. A force of 20 N acts on a mass of 4 kg. The acceleration produced is

• A. 0.2 m s-2
• B. 5 m s-2
• C. 16 m s-2
• D. 80 m s-2

Explanation: From F equal to ma, the acceleration is 20 divided by 4, which is 5 m s-2. The answer 80 comes from multiplying instead of dividing, and 0.2 from inverting the ratio. Always check that the units resolve to metres per second squared.

6. The action and reaction forces described by Newton's third law

• A. act on the same body and cancel out
• B. act on different bodies and therefore never cancel
• C. are unequal in magnitude
• D. act in the same direction

Explanation: The pair is equal in magnitude and opposite in direction but acts on two different bodies, which is why they cannot cancel each other and why motion is possible at all. When you push a wall, your force acts on the wall and the wall's force acts on you. Forces only cancel when they act on the same body.

7. For a projectile launched from level ground, the maximum range is obtained at a launch angle of

• A. 30 degrees
• B. 45 degrees
• C. 60 degrees
• D. 90 degrees

Explanation: Range is proportional to sine of twice the launch angle, which is largest when twice the angle is 90 degrees, so the angle itself is 45 degrees. This assumes level ground and no air resistance; in real conditions the optimum drops slightly below 45 degrees. A launch at 90 degrees goes straight up and returns to the starting point with zero range.

8. At the highest point of the path of a projectile, its velocity is

• A. zero in every direction
• B. horizontal only, with the vertical component zero
• C. vertical only
• D. equal to the launch velocity

Explanation: Gravity acts only vertically, so the horizontal component of velocity is unchanged throughout the flight while the vertical component falls to zero at the peak. The projectile is therefore still moving horizontally at the top, which is why its acceleration there is still g downwards even though the vertical velocity is momentarily zero.

9. Which of the following is a vector quantity?

• A. Speed
• B. Distance
• C. Displacement
• D. Time

Explanation: Displacement has both magnitude and direction, whereas distance records only how far was travelled with no direction attached. Speed is the scalar partner of velocity, and time has no direction at all. This is why a runner completing a circular track has covered a large distance but has zero displacement.

10. The SI unit of linear momentum is

• A. N s-1
• B. kg m s-1
• C. kg m s-2
• D. N m

Explanation: Momentum is mass times velocity, so its unit is kilogram metre per second. It is also equal to the newton second, since a newton is kg m s-2 and multiplying by a second gives kg m s-1. The unit kg m s-2 is the newton, a force, and the newton metre is the joule.