A simple pendulum of length 1 m has a bob of mass 100 g . At the...

Given:
Mass of the bob, $m = 100 \text{ g} = 0.1 \text{ kg}$
Length of the pendulum, $L = 1 \text{ m}$
Speed at the lowest point, $v = 1.4 \text{ m/s}$

At the lowest point of the path, the net force acting towards the center of the circular path provides the necessary centripetal force. The forces acting on the bob are the tension $T$ upwards and the weight $mg$ downwards.

$T - mg = \dfrac{mv^2}{L}$

T = m \left(g +\dfrac{v^2}{L}\right)

Taking $g = 9.8 \text{ m/s}^2$:

$T = 0.1 \times \left(9.8 + \dfrac{(1.4)^2}{1}\right)$

$T = 0.1 \times (9.8 + 1.96)$

$T = 0.1 \times 11.76 = 1.176 \text{ N}$

Rounding to one decimal place, we get $T \approx 1.2 \text{ N}$.