M1 modelling assumptions

hi for part c of this question, I thought that the string is modelled as a light string since the string does not have any mass however the only answer is that the string is inextensible. But surely it's also light right

Also for part e the last part , I don't get why fr would also decreed the reaction force. Fr does not act veritically . It is parallel to the plane. I thought adding fr would only decrease the weight but I don't get why it decrease R too..... Thanks.

Yes, the string would need to be light too.



Perpendicular (to plane) component of Reaction = mg cos 25

Since m decreases, so does the perpendicular component of the reaction.

Component parallel to the plane remains the same.

So, overall, the magnitude of the reaction decreases.

What paper is this from? Is it a real exam one?

hi for part c of this question, I thought that the string is modelled as a light string since the string does not have any mass however the only answer is that the string is inextensible. But surely it's also light right ?

Also for part e the last part , I don't get why fr would also decreed the reaction force. Fr does not act veritically . It is parallel to the plane. I thought adding fr would only decrease the weight but I don't get why it decrease R too..... Thanks.