Very basic motion law - Newton's 2nd

[2clients]

Homework Statement

a 5 kg object placed on a frictionless, horizontal table is connected to a string that passes over a pulley and then is fastened to a hanging 9 kg object. Find the acceleration of the two objects and the tension in the string.

Homework Equations

F = ma

The Attempt at a Solution

It just seems to me that if there is no friction the second object on the horizontal table should travel as the same speed that the 9.00 kg object falls. If there is no friction, then I don't see what force would be needed to "pull" the second object across the table, or how it would slow down the 9 kg object.

Thank you!

 

[LowlyPion]

Homework Statement

a 5 kg object placed on a frictionless, horizontal table is connected to a string that passes over a pulley and then is fastened to a hanging 9 kg object. Find the acceleration of the two objects and the tension in the string.

Homework Equations

F = ma

The Attempt at a Solution

It just seems to me that if there is no friction the second object on the horizontal table should travel as the same speed that the 9.00 kg object falls. If there is no friction, then I don't see what force would be needed to "pull" the second object across the table, or how it would slow down the 9 kg object.

Thank you!

Draw a diagram. If there is tension in the line then whatever force there is from gravity on the hanging weight will be used to accelerate both weights.

 

[baba89]

Your understanding is correct. According to Newton's Second Law, the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. In this scenario, the only force acting on the 5 kg object is the tension in the string, which is equal to the weight of the 9 kg object. Therefore, the acceleration of the 5 kg object will be equal to the acceleration due to gravity, which is 9.8 m/s^2. As for the tension in the string, it will also be equal to the weight of the 9 kg object, which is 9 kg x 9.8 m/s^2 = 88.2 N. This shows that the two objects will have the same acceleration and move at the same speed, as you correctly stated. The lack of friction on the table does not affect this result, as the tension in the string is still the only force acting on the 5 kg object.