# Physics Questions and Answers – Straight Line Motion – Average Velocity and Average Speed

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Straight Line Motion – Average Velocity and Average Speed”.

1. What will be the velocity v/s time graph of a ball falling from a height before hitting the ground look like?
a) A straight line with positive slope
b) A straight line with negative slope
c) A straight line with zero slope
d) A parabola

Explanation: As the ball falls down, its velocity increases. This is because of the acceleration due to gravity. Hence the graph looks like a straight line with positive slope. The first equation of motion verifies this.

2. Which of the following is the correct formula for average velocity?
a) v = dx/dt
b) v = x/t
c) v = xt
d) v = t/x

Explanation: The correct formula is v = x/t. Average velocity is total change in displacement divided by total change in time. v = dx/dt is the formula for instantaneous velocity.

3. A truck requires 3 Hrs to complete a journey of 150 km, what is the average speed?
a) 50 km/hr
b) 25 km/hr
c) 15 km/hr
d) 10 km/hr

Explanation: Average speed is defined as total distance divided by total time. The total distance is 150 km and total time taken is 3 Hrs, therefore average speed = 150/3 = 50 km/hr.

4. Average speed of a car between points A and B is 20 m/s, between B and C is 15 m/s, between C and D is 10 m/s. What is the average speed between A and D, if the time taken in the mentioned sections is 20s, 10s and 5s respectively?
a) 17.14 m/s
b) 15 m/s
c) 10 m/s
d) 45 m/s

Explanation: Average speed is the total distance divided by total time taken. Total displacement (d = vt) = 20×20 + 15×10 + 10×5 = 600 m. Total time = 20 + 10 + 5 = 35 s. Therefore, average speed = 600/35 = 17.14 m/s.

5. Which of the following statement is correct?
a) Average speed > Instantaneous speed
b) Average speed >= Instantaneous speed
c) Average speed <= Instantaneous speed
d) Average speed < Instantaneous speed

Explanation: Average speed is the ratio of total distance to total time. Instantaneous speed is the ratio of instantaneous change in distance to instantaneous change in time. Average speed can be equal to instantaneous speed but is usually less than that.

6. In a uniformly accelerated motion, the speed varies from 0 to 20 m/s in 4 s. What is the average speed during the motion?
a) 10 m/s
b) 20 m/s
c) 0 m/s
d) 15 m/s

Explanation: From first equation of motion we have, v = u + at, which implies that a = 5 m/s2. From second equation of motion we have s = ut + (1/2)at2, which implies that s = 40 m. Average speed = s/t = 40/4 = 10 m/s.

7. What happens to the average velocity when a body falls under gravity with terminal velocity?
a) It increases
b) It decreases
c) It remains constant
d) It changes exponentially

Explanation: When the body is moving with terminal velocity, the velocity does not change. It means that equal displacement is being covered in equal time intervals. Hence the average velocity remains constant.

8. A ball is thrown up in the sky. After reaching a height, the ball falls back. What can be said about the average velocity?
a) It is non zero
b) It is zero
c) It is greater than zero
d) It is less than zero

Explanation: The average velocity is zero. The ball covers positive displacement when it goes up and negative displacement when it comes down. Hence the total displacement is zero. Therefore, the average velocity is zero.

9. A car is moving around a tree in a circular path. What can be said about the average velocity?
a) It is non zero
b) It is zero
c) It is greater than zero
d) It is less than zero

Explanation: Take any point on the circular path. The car moves in a circle and hence will come back to the same point after a definite time interval. Therefore, the displacement is 0. Hence, the average velocity is zero.

10. The changes in displacement in three consecutive instances are 5 m, 4 m, 11 m, the total time taken is 5 s. What is the average velocity in m/s?
a) 1
b) 4
c) 7
d) 6 