Two boats $A$ and $B$, having the same speed relative to the river are moving in a river. The boat $A$ moves normal to the river current, as observed by an observer moving with the velocity of the river current. The boat $B$ moves normal to the river, as observed by the observer on the ground. Choose the incorrect options.

A ball is thrown from ground at an angle $\theta$ with horizontal and with an initial speed $u_0$. For the resulting projectile motion, the magnitude of average velocity of the ball up to the point when it hits the ground for the first time is $V_1$. After hitting the ground, the ball rebounds at the same angle $\mathrm{\theta }$ but with a reduced speed of $\frac{u_0}{\alpha }$. Its motion continues for a long time as shown in figure. If the magnitude of average velocity of the ball for entire duration of motion is $0.8V_1$, the value of $\mathrm{\alpha }$ is,

A particle has an initial velocity $3\hat{\mathrm{i}}+4\hat{\mathrm{j}}$ and an acceleration of $0.4\hat{\mathrm{i}}+0.3\hat{\mathrm{j}}$. Its speed after $10 \mathrm{s}$ is,