A body is thrown vertically upwards with a velocity of 35 $\mathrm{ms}^{-1}$ from the ground. The ratio of the speeds of the body at times 3 s and 4 s of its motion is (Acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )

• A

  $3: 4$
• Correct answer
  B

  $1: 1$
• C

  $2: 1$
• D

  $3: 2$

Solution

$\begin{aligned} \mathrm{u} & =35 \mathrm{~ms}^{-1} \\ \therefore \quad \mathrm{t}_1 & =\mathrm{t}_2=\frac{\mathrm{u}}{\mathrm{g}}=\frac{35}{10}=3.5 \mathrm{~s}\end{aligned}$ $\therefore$ The particle at time 3s and 4 s is at same level. $\therefore \quad \mathrm{v}_{2 \mathrm{~s}}=\mathrm{v}_{4 \mathrm{~s}} \Rightarrow \frac{\mathrm{v}_{2 \mathrm{~s}}}{\mathrm{v}_{4 \mathrm{~s}}}=1: 1$

Hence, the correct answer is option: 'B'.