A boy standing on road has to hold umbrella at 30° with vertical to keep the rain away. He throws umbrella and starts running at 10 km / hr he finds that rain drops are hitting his head vertically. The speed of raindrops w.r.t. ground is

Question

A boy standing on road has to hold umbrella at 30° with vertical to keep the rain away. He throws umbrella and starts running at 10 km / hr he finds that rain drops are hitting his head vertically. The speed of raindrops w.r.t. ground is (A) 10 km / h (B) 10 √3 km / h (C) 15 km / h (D) 20 km / h

Tardigrade Admin · Accepted Answer

<img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/9c05de06f2fff227bd76b1b82b394541-.png" /> vecvR g= vecvR m+ vecvm g From geometry (vm g/vR g)= sin 30° (10/vR g)= sin 30 ∴ VR g=10 × 2=20 km / h .

Q. A boy standing on road has to hold umbrella at $3 0^{\circ}$ with vertical to keep the rain away. He throws umbrella and starts running at $10 km / h r$ he finds that rain drops are hitting his head vertically. The speed of raindrops w.r.t. ground is

$10 km / h$

$103 km / h$

$15 km / h$

$20 km / h$

$v_{R g} = v_{R m} + v_{m g}$
From geometry $\frac{v _{m g}}{v _{R g}} = sin 3 0^{\circ}$
$\frac{10}{v _{R g}} = sin 30$
$∴ V_{R g} = 10 \times 2 = 20 km / h .$

Q. A boy standing on road has to hold umbrella at 30∘ with vertical to keep the rain away. He throws umbrella and starts running at 10km/hr he finds that rain drops are hitting his head vertically. The speed of raindrops w.r.t. ground is

10km/h

103​km/h

15km/h

20km/h