Exams › JEE Main › Physics

Water of density rho flows through a fire hydrant at a volume flow rate L. The water rises vertically inside the hydrant and then turns through 90 degrees to leave horizontally with speed V. The pipe has the same uniform cross-section throughout. Find the magnitude of the force exerted by the water on the bend (corner) of the hydrant.

1. rho*V*L
2. zero
3. 2*rho*V*L
4. sqrt(2)*rho*V*L

Correct answer: sqrt(2)*rho*V*L

Solution

Mass flow rate = rho*L. Incoming momentum is vertical (rho*L*V upward) and outgoing is horizontal (rho*L*V). The force on the water has components rho*L*V in each direction, magnitude sqrt(2)*rho*L*V. By Newton's third law the water exerts the same magnitude on the corner.

Related JEE Main Physics questions

• Which of the following has the same SI unit as impulse?
• A monkey slides downward from a tree branch with uniform acceleration. If the maximum tension the branch can withstand is 75% of the monkey’s weight, what is the least downward acceleration that will allow the monkey to descend without snapping the branch?
• A 1000 kg car is travelling at 30 m/s. The brakes are applied until it stops. If the friction force between the tyres and the road is 5000 N, how long will the car take to come to rest?
• A rocket initially ejects gas from its rear at a mass rate of 0.1 kg s⁻¹. If the exhaust speed relative to the rocket is 50 m s⁻¹ and the rocket’s mass is 2 kg, what is its acceleration in m s⁻²?
• A block of mass M rests on a rough level floor with coefficient of friction μ. A person applies a horizontal pull, but the block remains at rest. If the total contact force exerted by the floor on the block is F, then
• Which of the following types of motion on a frictionless plane surface occurs without any force acting on the body?

⚔️ Practice JEE Main Physics free + battle 1v1 →