A block is projected with speed \( 20 \mathrm{~m} / \mathrm{s} \) o...

A block is projected with speed \( 20 \mathrm{~m} / \mathrm{s} \) on a rough horizontal surface. The coefficient of friction \( (\mu) \)
P between the surfaces varies with time \( (t) \) as shown in figure. The speed of body at the end of 4 second will be \( \left(g=10 \mathrm{~m} / \mathrm{s}^{2}\right) \)
(1) \( 2 \mathrm{~m} / \mathrm{s} \)
(2) \( 5 \mathrm{~m} / \mathrm{s} \)
(3) \( 7.2 \mathrm{~m} / \mathrm{s} \)
(4) \( 9.5 \mathrm{~m} / \mathrm{s} \)