Can an object have zero velocity and non-zero acceleration at the same time? Give examples.
Yes, an object can have zero velocity and still be accelerating.
Velocity is a vector quantity and is defined as the time rate of change of displacement of an object. On the other hand, acceleration is the time rate of change of velocity.
Suppose an object is moving in the forward direction. A force starts acting on it in the opposite direction of its motion. It decreases the velocity of the object and continues to do so until it approaches zero.
While observing the object, you will see that it starts accelerating in the reverse direction due to the force. At this point, the velocity becomes zero. And at any time before and after this point, the velocity is non-zero.
The change in velocity continues even when the object acquires zero velocity. Thus, acceleration occurs simultaneously.
For example, a ball is projected upward from the surface of the Earth with a constant velocity. The force of gravitation acts opposite (downward) to the motion of the ball. At the highest point, the velocity of the ball becomes zero, and the ball starts falling with an acceleration of .
According to the rule of thumb, every five seconds between a lightning flash and the following thunder gives the distance to the flash in miles.
(a) Assuming that the flash of light arrives in essentially no time at all, estimate the speed of the sound in m/s from this rule.
(b) What would be the rule for kilometers?
An automobile traveling at 95 km/h overtakes a 1.30 km long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h, how long does it take for the car to pass it, and how far will the car have traveled in this time? See Fig. 2-36. What are the results if the car and the train are traveling in opposite directions?
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