Power
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See all →- At any instant of time t, the displacement of any particle is given by 2t-1 (SI unit) under the influence of force of 5N. The value of instantaneous power is (in SI unit): Answer: 2. 10 Key idea: Instantaneous power P=vec F·vec v . Velocity v=d/dt(2t-1)=2 m/s (constant). Then P=Fv=5×2=10 W. Option 2. 1
- An electric lift with a maximum load of 2000 kg (lift + passengers) is moving up with a constant speed of 1.5 ms^-1. The frictional force opposing the motion is 3000 N. The minimum power delivered by the motor to the lift in watts is : (g = 10 ms^-2) Answer: 4. 34500 At constant speed the motor force balances weight plus friction. F=mg+f=2000×10+3000=23000\ N P=Fv=23000×1.5=34500\ W Optio... 1
- Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional force are 10% of the input energy. How much power is generated by the turbine ? (g = 10 m/s^2) Answer: 2. 8.1 kW Key idea: power input = (mass per second) × g × h; the turbine gets 90% of it. P_in=15×10×60=9000\ mathrm W P_out=0.9×9000... 1