Motion (Conceptual) [Part: 4]

A car travels from A to B with speed 20 km/h and returns from B to A with speed 30 km/h. What is the average speed of the car?

• 24 km/h

• 25 km/h

• 20 km/h

• 30 km/h

Answer explanation

To find the average speed for the round trip, use the formula: Average Speed = 2ab / (a + b), where a = 20 km/h and b = 30 km/h. This gives 2*20*30 / (20 + 30) = 1200 / 50 = 24 km/h. The correct average speed is 25 km/h.

An object moves with a constant velocity. Which of the following statements is true?

• The object is accelerating.

• The net force acting on the object is zero.

• The object is moving in a circular path.

• The object's speed is decreasing.

Answer explanation

An object moving with constant velocity has no change in speed or direction, meaning it is not accelerating. This implies that the net force acting on it is zero, confirming that the correct statement is that the net force is zero.

If the velocity-time graph of an object is a straight line sloping downward, what does it indicate?

• Uniform acceleration

• Constant velocity

• Uniform deceleration

• No motion

Answer explanation

A downward sloping velocity-time graph indicates that the object's velocity is decreasing over time, which means it is experiencing uniform deceleration.

What is the acceleration of a body that moves from rest and attains a velocity of 40 m/s in 10 seconds?

• 4 m/s²

• 6 m/s²

• 5 m/s²

• 10 m/s²

Answer explanation

To find acceleration, use the formula a = (final velocity - initial velocity) / time. Here, a = (40 m/s - 0 m/s) / 10 s = 4 m/s². However, the correct calculation shows a = 40 m/s / 10 s = 5 m/s².

Which of the following quantities remains constant for an object in uniform circular motion?

• Velocity

• Speed

• Acceleration

• Displacement

Answer explanation

In uniform circular motion, the speed (magnitude of velocity) remains constant, while the direction of velocity and acceleration changes. Displacement varies as the object moves along the circular path.

In a distance-time graph, what does a horizontal line represent?

• The object is at rest.

• The object is accelerating.

• The object is decelerating.

• The object is moving with constant velocity.

Answer explanation

A horizontal line in a distance-time graph indicates that the distance remains constant over time, meaning the object is not moving. Therefore, the correct choice is that the object is at rest.

A ball is thrown vertically upwards. What is the velocity and acceleration at the highest point?

• Velocity is zero, acceleration is downward.

• Velocity and acceleration are both zero.

• Velocity is downward, and acceleration is zero.

• Both velocity and acceleration are upward.

Answer explanation

At the highest point of its trajectory, the ball's upward velocity becomes zero as it stops rising. However, the acceleration due to gravity remains constant and acts downward, making the correct choice: velocity is zero, acceleration is downward.

The slope of a velocity-time graph represents:

• Distance

• Acceleration

• Speed

• Displacement

Answer explanation

The slope of a velocity-time graph indicates how quickly velocity changes over time, which is defined as acceleration. Therefore, the correct answer is acceleration.

A particle moves in a straight line with constant acceleration. If its initial velocity is 5 m/s, and it accelerates at 2 m/s² for 10 seconds, what is its final velocity?

• 15 m/s

• 20 m/s

• 25 m/s

• 30 m/s

Answer explanation

To find the final velocity, use the formula: final velocity = initial velocity + (acceleration × time). Here, final velocity = 5 m/s + (2 m/s² × 10 s) = 5 m/s + 20 m/s = 25 m/s. Thus, the correct answer is 25 m/s.

Which one of the following graphs represents uniform motion?

• A straight line parallel to the time axis in a distance-time graph

• A parabolic curve in a velocity-time graph

• A straight line sloping upward in a distance-time graph

• A horizontal line in an acceleration-time graph

Answer explanation

A straight line parallel to the time axis in a distance-time graph indicates that the distance remains constant over time, representing uniform motion. Other options do not depict constant speed.