The fact that the question states an assumption of massless pulley and string is to “idealise the situation”. Lots of physics problems ask you to ignore factors that are not particularly relevant to the point of the question. Here, you are asked to consider the forces and motion of the masses only. From there you are to determine the motion of the masses. If the question stated otherwise then this would create another level of complexity which is not consistent with level of physics you are studying and the physics being currently taught to you.

The fact that the question states an assumption of massless pulley and string is to “idealise the situation”. Lots of physics problems ask you to ignore factors that are not particularly relevant to the point of the question. Here, you are asked to consider the forces and motion of the masses only. From there you are to determine the motion of the masses. If the question stated otherwise then this would create another level of complexity which is not consistent with level of physics you are studying and the physics being currently taught to you.

But to answer your question, the string is attached to a mass and the mass experiences a force (and therefore acceleration) meaning the string will accelerate as well.

The fact that the question states an assumption of massless pulley and string is to “idealise the situation”. Lots of physics problems ask you to ignore factors that are not particularly relevant to the point of the question. Here, you are asked to consider the forces and motion of the masses only. From there you are to determine the motion of the masses. If the question stated otherwise then this would create another level of complexity which is not consistent with level of physics you are studying and the physics being taught to you.

The fact that the question states an assumption of massless pulley and string is to “idealise the situation”. Lots of physics problems ask you to ignore factors that are not particularly relevant to the point of the question. Here, you are asked to consider the forces and motion of the masses only. From there you are to determine the motion of the masses. If the question stated otherwise then this would create another level of complexity which is not consistent with level of physics you are studying and the physics being currently taught to you.