If the petrol burnt per hour in driving a motor boat varies as the cube of it's velocity when going against a current of `C` .KMPH the most economical speed is

Assuming the petrol burnt (per hour) in driving a motor boat veries as the cube of its velocity,show that the most economical speed when going against the current of c miles per hour is ((3c)/(2)) miles per hour.

A motor boat takes 2 hours to travel a distance of 9 km downstream and it takes 6 hours to travel the same distance against the current. The speed of the boat is still water and that of the current (in km/h) respectively are :

A motor boat takes 2 hours to travel a distance of 9 km downstream and it takes 6 hours tomtravel the same distance against the current.The speed of the boat in still water and that of the current (in km/h) respectively are:

A motorboat takes 2 hours to travel a distance of 9 km down the current and it takes 6 hours to travel the same distance against the current. What is the speed of the boat in still water in kmph?

A boat goes 6km an hour in still water,it takes thrice as much time in going the same distance against the current in comparison to direction of current The speed of the current (in km/hour) is

A truck is to be driven 300 km on a highway at a constant speed of.x kmph. Speed rules of the highway required that 30<=x<=60 . The fuel costs Rs. 10 per litre and is consumed at the rate of 2+x^2/600 litres per hour. The wages of the driver are Rs. 200 per hour. The most economical speed to drive the truck, in kmph, is

A man in a boat crosses a river from point A. If he rows perpendicular to the banks he reaches point C (BC = 120 m) in 10 min. If the man heads at a certain angle alpha to the straight line AB (AB is perpendicular to the banks) against the current he reaches point B in 12.5 min. Find the width of the river w, the rowing velocity u, the speed of the river current v and the angle alpha . Assume the velocity of the boat relative to water to be constant and the same magnitude in both cases.

A fan operates at 200 volt (DC) consuming 1000W when running at full speed . It's internal wiring has resistance 1 Omega . When the fan runs at full speed , its speed becomes constant. This is because the torque due to magnetic field inside tha fan is balanced by the torque due to air resistance on the blades of the fan and torque due to friction between the fixed part and the shaft of the fan. The electrical power going into the fan is spent (i) in the internal resistance as heat, call it P_(1)(ii) in doing work against internal friction and air resistance producing heat, sound etc. call it P_(2) . When the coil of fan rotates, an emf is also induced in the coil. This opposes the external emf applied to snd the current into the fan. This emf is called back-emf,call it 'e' . Answer the following questions when the fan is running at full speed. The value of power P_(1) is