For each of the cases listed below, decide whether or not the motion described is an example of acceleration: (t/f)

1) a roller coaster as it starts to roll down the track
2) a ball tossed straight up, at the peak of its trajectory
3) a planet tracing out a circular orbit at a constant speed
4) a block sliding down a straight ramp at a constant speed
5) an airplane skidding to a stop on a runway
6) a dump truck carrying a load straight forward at a constant speed

1. True

2. True

3. False

4. False

5. True

6. False

Explanation:

Acceleration: It refers to the change in velocity/speed of an object with respect to time. When the speed increases with time we call it acceleration and when its decreases it is called as deceleration.  Let us analyze each instance individually:

1. When roller coaster starts to roll down the track its speed will increase with time. That means it is accelerating.

2. When the ball reaches at the peak of its trajectory, it comes to a stop for a fraction of a second that means it decelerates.

3. Since the velocity remains constant there is no acceleration.

4. Since the speed is no changing with time, there is no acceleration.

5. Since the moving plane comes to a stop, it is a case of deceleration.

6. Since the truck is moving at a constant speed so the acceleration is zero.

what is the speed of a softball that travels 20m in 2secs

speed = 20/2 = 10 m/s