Question

A particle is thrown vertically up with speed u so that distance covered in last second of flight is $35m$ . If then initial speed of throw is

• A. $20m/s$
• B. $26.45m/s$
• C. $40m/s$
• D. $50m/s$

Answer 1

The correct option is A $20m/s$

We know from equation of motion we get,

$v=u-gt$-------(1)

as velocity of the particle becomes at the very last second of flight $v=0$

Thus equation 1 can be written as,

$t=\frac{u}{g}$-------(A)

Again we know,

$s=ut-\frac{1}{2}g{t}^2$

$35=\frac{u^2}{g}-\frac{1}{2}g{\left(\frac{u}{g}\right)}^2$

$u=\sqrt{700}=26.45$