Motion on frictionless plane

Classical Mechanics Level 2

In the above diagram, object $A$ is on a frictionless horizontal plane and is connected to object $B$ by a string and a pulley. What is the tension force on the string when both $A$ and $B$ start to move?

Gravitational acceleration is $g= 10 \text{ m/s}^2.$

\frac{40}{3} \text{ N}

20 \text{ N}

40 \text{ N}

\frac{20}{3} \text{ N}

2 solutions

Krishna Karthik
Apr 8, 2020

The net force acting on block B with $m = 4$ Kgs is equal to the gravitational force impeded by the tension force from the string.

We can write it as follows: $m_B a = m_B g - T$

We can find the total acceleration of the system by using $F = ma$ again, which is the gravitational force acting on block B divided by the total mass of the system which it is affecting:

$m_B g = (m_B+m_A) a$

By substituting the values in, we get $a = \large \frac{40}{6}$ $m/s^2$

Substituting this value of $a$ into the first equation relating the tension force with the force on object B,

we get $T= \large \frac{40}{3} N$

Satvik Pandey
Aug 19, 2014

Let the accelerations of the blocks be 'a'. So 4g-T=4a and T=2a (using Newton's 2nd law) On solving we gat T=40/3 (assuming g=10m/s^2)

Motion on frictionless plane

2 solutions

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