A uniform motion of a car along a circular path experiences
- A.a change in speed due to a change in its direction of motion.
- B.a change in velocity due to a change in its direction of motion.
- C.a change in momentum due to no change in its direction of motion.
- D.a constant momentum due to a change in its direction of motion.
Correct answer
Explanation
The correct answer is B, a change in velocity due to a change in its direction of motion. In uniform circular motion the speed stays the same, but the direction changes at every point, so the velocity keeps changing.
Velocity is a vector: it has both size and direction. A car going round a circular track at a steady 40 km/h has a constant speed, yet its direction is always along the tangent and keeps turning. A changing velocity means the car is accelerating, and this centripetal acceleration points towards the centre of the circle. The force behind it, here the friction between the tyres and the road, is the centripetal force.
A is wrong because the speed is uniform, so it does not change. C is wrong because the direction does change, and that is why momentum changes. D is wrong because momentum, being mass times velocity, also changes when the direction changes.
Exam tip: uniform circular motion means constant speed, changing velocity, so it is accelerated motion.
Practice Questions
View allWhich of the following statements about electromagnetic waves, sound waves and water waves is/are correct ? 1. They exhibit reflection 2. They carry energy 3. They exert pressure 4. They can travel in vacuum Select the correct answer using the code given below :
- A.1,2 and 3
- B.2 and 4
- C.1 and 3 only
- D.1 only
Show answer
All three kinds of wave reflect, carry energy and exert pressure, but only electromagnetic waves can travel through a vacuum.
Read the full explanation →Which one of the following is NOT the unit of energy?
- A.Joule
- B.Watt-hr
- C.Newton-metre
- D.kg-metre/sec²
Show answer
A kilogram-metre per second squared is mass times acceleration, which is force; it is the newton, not a unit of energy.
Read the full explanation →To protect steel and iron from rusting, a thin layer of which one of the following metals is applied?
- A.Magnesium
- B.Zinc
- C.Aluminium
- D.Lead
Show answer
Coating iron or steel with a thin layer of zinc is called galvanisation, and it is the most common way to protect them from rusting.
Read the full explanation →In an electric circuit, a wire of resistance 10 Ω is used. If this wire is stretched to a length double of its original value, the current in the circuit would become :
- A.half of its original value.
- B.double of its original value.
- C.one-fourth of its original value.
- D.four times of its original value.
Show answer
Stretching the wire to twice its length makes its resistance four times larger, so at the same voltage the current falls to a quarter.
Read the full explanation →Which one of the following scientists mentioned that an electron in an atom could revolve in certain stable orbits without the emission of radiant energy ?
- A.Ernest Rutherford
- B.J.J. Thomson
- C.Niels Bohr
- D.Albert Einstein
Show answer
In his 1913 model of the atom, Bohr proposed that electrons move in certain fixed orbits, called stationary states, in which they do not radiate energy.
Read the full explanation →