The formula to calculate the change in the magnetic flux associated with the given loop can be written as

$\begin{array}{rcl}∆\varphi & =& -BA\cos \theta \\ & =& -B\left(lb\right)\cos \theta ...\left(1\right)\end{array}$

The formula to calculate the induced emf is given by

$\begin{array}{rcl}\epsilon & =& -\frac{∆\varphi }{∆t}\\ & =& \frac{B\left(lb\right)\cos \theta }{∆t} ...\left(2\right)\end{array}$

From equation (2), it follows that

$\begin{array}{rcl}\epsilon & =& \frac{4\times \left(2.5\times 2\right)\times \cos 60°}{10} \mathrm{V}\\ & =& 1 \mathrm{V}\end{array}$