Question

(a) Which of the following do you see moving with constant velocity? (1) A ship sailing northeast at a speed of 5 meters per second (2) The Moon orbiting the Earth (3) A tennis ball traveling across the court after having been hit by a tennis racket (4) A can of soda sitting on a table (5) A person riding on a Ferris wheel that is turning at a constant rate. (b) In which of the following situations is there observational evidence for significant interaction between two objects? How can you tell? (1) A ball bounces off a wall with no change in speed. (2) A baseball that was hit by a batter flies toward the outfield. (3) A communications satellite orbits the Earth. (4) A space probe travels at constant speed toward a distant star. (5) A charged particle leaves a curving track in a particle detector.

Short answer

1. Only (1)and (4) parts are the cases where the bodies are moving with constant velocities.
2. Observational evidence for significant interaction is present in parts, (1),(2),(3) and(5).

Step-by-step solution

Understanding the concept of constant velocity

A body is said to be in constant velocity when its speed, as well as direction, is constant.

If any of the above conditions is not satisfied, the body is said to be having variable velocity.

If the body is not having constant velocity, it can be concluded that it has significant interactions with the surroundings

Analyzing each statement in part (a)

(1) When the ship is sailing at a speed of meters per second in the northeast direction, its speed and direction of movement are constant. Hence, its velocity is constant.

(2) In this case, the moon is orbiting the Earth. Its direction of motion changes every second. Hence, its velocity is not constant.

(3) After the ball is hit by the tennis racket, its speed will change. Its direction would also change when it travels through the court. Hence, its velocity is not constant.

(4) The can of soda is sitting on a table. It is in a rest state.The resting state is a special case of uniform motion. Hence, its velocity is constant.

(5) The Ferris wheel is turning at a constant speed, but its direction changes every second. Hence, its velocity is not constant.

Thus, out of all the given cases, only and are the cases of constant velocity.

Analyzing each statement in part (b)

(1) After hitting the wall, its direction will get reversed. So, you can tell that its velocity is changing. Hence, there is significant interaction.

(2) Both the direction and speed of the ball will change when it is hit by the batter. Hence, there is significant interaction between the ball and the bat.

(3) Since the satellite orbits the Earth, it moves in a circular path. Its velocity is constantly changing due to changes in direction. So, it interacts with its surroundings.

(4) In this case, the speed and direction both are constant. So, there is no interaction with the surrounding.

(5) Its direction is changing. So, there is interaction with the surroundings.

Thus, out of all the given cases, (1),(2),(3) and (5) had significant evidence to prove there was an interaction between two bodies.