Advertisements
Advertisements
Question
Calculate the power of a crane in watts, which lifts a mass of 100 kg to a height of 10 m in 20s.
Advertisements
Solution
According to the problem, mass = m= 100 kg height = h – 10 m, time interval, t = 20 s. Power is the rate of doing work with respect to time.
We know from the formula that, the power = work done/time = `(Fds cos θ)/(time)`
F = mgh
mg = 100 × 10 = 1000
h = 10 m
t = 20s
θ = 0, as the force and the displacement, are in the same direction.
Hence power = `(1000 xx 10 cos 0)/20` = 500 watts
APPEARS IN
RELATED QUESTIONS
A pump on the ground floor of a building can pump up water to fill a tank of volume 30 m3 in 15 min. If the tank is 40 m above the ground, and the efficiency of the pump is 30%, how much electric power is consumed by the pump?
The blades of a windmill sweep out a circle of area A.
- If the wind flows at a velocity v perpendicular to the circle, what is the mass of the air passing through it in time t?
- What is the kinetic energy of the air?
- Assume that the windmill converts 25% of the wind’s energy into electrical energy, and that A = 30 m2, v = 36 km/h and the density of air is 1.2 kg m–3. What is the electrical power produced?
Power P= ............ /time taken.
1 H.P. = .........
Match the following
| column A | Column B |
| A stone at a height | power |
| A Moving ball | joule |
| Energy | work done in 1 s |
| Power | potential energy |
| Watt | kinetic energy |
Two coolies A and B do some work in time 1 minute and 2 minute respectively. The power spent is
The expression of power P is
A pump raises water by spending 4×105J of energy in 10s. Find the power of the pump.
It takes 20 s for a girl A to climb up the stairs while girl B takes 15 s for the same job. Compare the work done .
It takes 20 s for a girl A to climb up the stairs while girl B takes 15 s for the same job. Compare the power spent by then.
Define power.
A wind-powered generator converts wind energy into electric energy. Assume that the generator converts a fixed fraction of the wind energy intercepted by its blades into electrical energy. For wind speed v, the electrical power output will be proportional to ______
Arrive at an expression for power and velocity. Give some examples for the same.
A bullet of mass 20 g strikes a pendulum of mass 5 kg. The centre of mass of the pendulum rises a vertical distance of 10 cm. If the bullet gets embedded into the pendulum, calculate its initial speed.
An engine develops 20 kW power. How much time will it take to lift a mass of 200 kg to a height of 50 m? (g = 10 m/s2)
An engine pumps up 200 kg of water through a height of 20 m in 10 seconds. If the efficiency of the engine is 80%. Calculate the power of the engine.
A man is throwing bricks of mass 2 kg onto a floor from a height of 2 m. Bricks reach the floor at a speed `2sqrt(10)` m/s. Man throws 10 bricks in a minute. If the power of man is W watt then `3/10` W is equal to ______ W.
Sand is being dropped from a stationary dropper at a rate of 0.5 kgs-1 on a conveyor belt moving with a velocity of 5 ms-1. The power needed to keep belt moving with the same velocity will be ______.
Name the quantity which is measured in kW.
