 Let's solve a couple of questions on velocity and speed. For the first one, we have the instantaneous speed of an object at point P is 5 meters per second. Which of these describes the meaning of 5 meters per second most accurately? And it's, there's a note which says 1 nanometers, this is equal to 10 to the power minus 9 meters and 1 nanoseconds, it is 10 to the power minus 9 seconds. Okay pause the video, read the options and try this one on your own first. All right, hopefully you have given this a shot. Now we need to choose one answer. So let's start reading the options. The option, the first one says object covered 5 meters in a time interval of one second near point P. So let's say this is point P, then in one second, the object covered 5 meters. And we need to think about if this statement is the most accurate description of, of this one, that the instantaneous speed of an object at point P is 5 meters per second. Now this could be the most accurate description if the object was moving with a constant speed, constant speed of 5 meters per second. Then we can say, yes, that the object will cover 5 meters in a time interval of one seconds near point P, but we don't really know that. We just know the instantaneous speed of an object at point P. So just at the instant when the object is at point P, there, the speed is 5 meters per second. We do not know what the speed is after point P or before point P. So we don't have that information. And therefore we cannot really say that the object will cover 5 meters in a time interval of one seconds. This is not the most accurate description of only this statement, instantaneous speed 5 meters per second. Second one says, object covered 5 nanometers in a time interval of one nanoseconds near point P. So this would mean, this would mean that before or after in a very, very, very small time interval for one nanoseconds, the object is covering a distance of 5 nanometers. This would mean, so if, if we write, if we write 0.000134567895 nanometers divided by one nanosecond. One, two, three, four, five, six, seven, eight, nine, one nanosecond. So we can see still that the ratio still comes out to be equal to 5 meters per second. So this could very well be true that the near point P, if the instantaneous speed of an object at point P is 5 meters per second. So near point P, it is covering a distance of 5 nanometers in an interval of one nanoseconds. So when talking about instantaneous speed, we need to look at the distance covered in a very, very small time interval of time around the point P to get an accurate picture. Now, the smaller the time interval, the more accurate our description. And since one nanosecond is smaller time interval than one second, this option, this option is more accurate than the first option. In the first option, this statement will only be true if the object is moving with a constant speed. But if the speed of an object is changing, then we need to look at the distance covered in a very small interval of time around point P to get an accurate picture. And the smaller the time interval, more accurate as a description. Option C says both descriptions are equally valid. Both descriptions would have been equally valid if the object was moving with a constant speed of 5 meters per second throughout. But if the speed of the object is changing, then we need to look at the distance covered in a small time interval around point P to get an accurate picture. This one is also wrong. All right, let's move on to the next one now. Here we have a particle which is moving on a straight line path and its net displacement, its net displacement in a time T is zero. Choose the option that best describes a velocity V at time T and the average velocity V average in time T. We need to choose one answer. Again pause the video, give this one a try. All right. So here we need to think about instantaneous velocity, that is the velocity at time T and the average velocity V average. And we know that net displacement is zero. So if you try to show this kind of motion, if there is, let's say a particle moving in a straight line path and then it moved somewhat ahead, then it started moving back. And here at this point, when it comes back to the initial position, the initial and the final position, they're on top of each other. So net displacement is really just zero. Net displacement is zero. But we don't know if the object is at rest, rest or moving. We do not know if the object is at rest or if it's moving when it came back to its initial position. There is no information around that in the question. Okay. Now let's see what the options are. First one says instantaneous velocity is zero and average velocity may or may not be zero. Well, we don't know if the instantaneous velocity is zero or if it's some number, if it has a magnitude, that information is not given in the question. So first statement in itself is not right. And the second one says V average may or may not be zero. Well, V average, what is V average? Let's write it down. V average would be net displacement. Average velocity is really the net displacement divided by the time taken, divided by the time taken. Net displacement here is zero. So V average would just be zero. So again, the second option is also wrong. B1 says V may or may not be zero and V average is zero. We just discussed that V, the instantaneous velocity at this point, object could be moving. It could be at rest. We do not really know. So this part makes sense. And V average is zero because the net displacement is zero. So option V is the right one and we need to choose one answer. But still let's look at the other two options. Both V and V average may or may not be zero. Well, this is true for instantaneous velocity because it could be moving or at rest, but V average is zero. We just calculated it. And the last one says both V and V average are equal to zero. Again, this is wrong because V, we do not know if instantaneous velocity at that particular time instant, at this very instant. We do not know if it is zero or if it has some magnitude. So V average is zero, but V is not. And therefore option D is also wrong. You can try more questions from this exercise in this lesson. And if you're watching on YouTube, do check out the exercise link, which is added in the description.