2. True or False (Write T if you think it is right....

2. True or False (Write T if you think it is right. Otherwise, write F.) 1) Velocity is the first derivative of position vector and acceleration is the second derivative of displacement vector. 2) The displacement is dependent on the choice of origin. 3) The only difference between velocity and speed is that one is a vector and the other a scalar. So magnitude of average velocity always equals average speed. 4) In projectile motion, the total force is always constant. 5) The velocity is dependent on the choice of reference frame. 6) If a man sits on the ground, his gravity and the support force by the ground are action-reaction pair. 7) In noninertial frame of reference, the direction of inertial force is the same direction as the accelaration of the reference frame. 8) Power represents the efficiency of work.

Transcript

00:01 So we've got some true or false questions here, so let's go through them in turn.

00:03 Now one i think is actually potentially the hardest in the sense that it depends on how you define the origin.

00:11 So velocity is the first derivative of the displacement vector with respect to time.

00:19 Now the position vector and the displacement vector can be the same depending on where you define your origin.

00:27 So if you define the origin as the point where you started, not necessarily the zero, but the point where you started the motion or when you want to measure the velocity from, then the position vector with respect to that origin depending on time, if you differentiate that, then you will get velocity.

00:44 So i'm going to say true, assuming that this position vector encodes your position dependent on time with respect to where you started from.

00:54 And then the acceleration is the second derivative of the displacement vector.

00:57 That's true.

00:59 Or it's the derivative, the first derivative of the velocity vector.

01:04 Then question two, the displacement is dependent on choice of origin.

01:08 That's false, right? because displacement is just a difference.

01:11 So it's a difference between the point where you end up and the point where you begin, and that should be independent of where the choice of origin is.

01:22 Three, the only difference between velocity and speed is that one is a vector and the other is a scalar.

01:27 That's true.

01:28 So velocity is just speed, but with a direction.

01:30 And so the magnet is, of velocity is going to be the magnitude of the speed.

01:33 So this is true.

01:37 Question four.

01:38 In projectile motion, the total force is always constant.

01:41 This is also true.

01:42 So in projectile motion, the only force acting anywhere is the object's weight.

01:47 Okay? and so this remains constant because the weight of the object doesn't change.

01:59 Question five, the velocity is dependent on the choice of reference frame.

02:03 This is also true...

Question

Please give Ace some feedback