Question

MC Question - please see attachment! - Answer is A, but how?

Answer 1

Tension acts on both sides of the pulley.

Answer 2

@Vincent-Lyon.Fr Yeah, I figured that part out, but I'm not sure how I should write my equation...?

Answer 3

The object is being lifted upward with a speed of 2m/s
so what do u think is the net force on the object?

Answer 4

2m?

Answer 5

Unit of force is Newtons
and could u explain how u got that?

Answer 6

Not sure really, I said that the speed should be multiplied by the mass, but that can't be right because the units wouldn't work out. I'm not sure how to get it.

Answer 7

If a body's centre of mass moves at constant velocity, what do Newton's laws tell you?

Answer 8

That it will remain at constant velocity unless it's compelled to change by a force

Answer 9

You said: "Not sure really, I said that the speed should be multiplied by the mass, but that can't be right because the units wouldn't work out. I'm not sure how to get it."

Do NOT invent your own theorems, go back to basics, i.e. Newton's laws of motion.

Answer 10

"That it will remain at constant velocity unless it's compelled to change by a force"

So, as long as this motion is going on, what is the net force acting on the body?

Answer 11

Since the net force is the overall force of an object, and we have constant velocity, how can we find the net force? I don't understand

Answer 12

force on pulley is
2t - mg = ma (newton second law )
2t - mg = (0)a (pulley is massless )
2t-mg = 0
2t = mg
t=mg/2

Answer 13

@vbosco Where are you getting the 2t from? Like what was the 'original formula' for it?

Answer 14

There is no such thing as 'original formula'. Re-read what I said before:
"Tension acts on both sides of the pulley."

Answer 15

The important thing here that you seem to miss is that since the centre of mass has constant velocity, then the net force on the body is NECESSARILY zero.

Answer 16

Let's say that t1 is different from t2. It would mean that the pulley would be rotating which is not true. If that were a case, then you should say, ok, then t1-t2 = ma, where m is the mass of the rope. But we know that rope is massles so m is 0 that means a should be infinite which is physical nonsense(a= (t1-t2)/0 ) That's why t1=t2=t, and since the center of mass is moving with constant velocity the sum of all forces acting on an object must be equal to zero. so t+t-mg=0 so t=mg/2