A stream of water strikes a stationary turbine blade. The incident water stream has a velocity of +18.0 m/s and the exiting stream has a velocity of –18.0 m/s. The water strikes the blade at a rate of 25.0 kg/s. Find the net force acting on the water and on the blade.
assuming the incident and exiting streams are 180 degrees, net change in velocityis 36m/s
force=impulse/time= mass/time*change velociyt=25kg/s*36m/s
remember that force= kg-m/s^2
force=36*25 N
Im not sure I understand. The book gives me two different answers, one is negative one is positive
please explain
To find the net force acting on the water and on the blade, we need to calculate the change in momentum.
The change in momentum of water is given by the equation:
Change in momentum = (mass of water) * (change in velocity)
Given that the mass of water per second is 25.0 kg/s and the change in velocity is (–18.0 m/s) – (+18.0 m/s) = –36.0 m/s, we can substitute these values into the equation:
Change in momentum of water = 25.0 kg/s * (–36.0 m/s) = –900 kg·m/s
Since momentum is a vector quantity, the negative sign means that the change in momentum is in the opposite direction of the initial velocity.
Now, the net force acting on the water can be determined using the equation:
Net force = change in momentum / time
Since the mass of water per second is given, time is equal to 1 second:
Net force on water = –900 kg·m/s / 1s = –900 N (negative indicates that it is in the opposite direction of initial velocity)
The net force acting on the blade is equal in magnitude but opposite in direction to the net force on the water. Thus, the net force acting on the blade is +900 N.