Advertisements
Advertisements
प्रश्न
A girl of mass 40 kg runs a height of 80 stairs, each 25 cm high with a load of 20 kg on her head in 25 sec. If g is 10 m/s2, find:
(i) Gravitational force acting on the girl.
(ii) Work done by her.
(iii) Useful work done by her.
(iv) Her power in watt.
Advertisements
उत्तर
(i) Gravitational force acting on the girl = Her mass in kg × g
= 40 × 10 = 400 N.
(ii) Total gravitational force = (Mass of girl + load) × g
= (40 + 20) × 10 = 600 N.
and Distance or height =`(80xx25)/100` = 20 m.
∴ Work done by her = 600 N × distance
∴ Total work done = 600 N × 20 m = 12000 J.
(iii) Useful work done = Load × g × Distance covered
= 20 × 10 × 20 = 4000 J.
(iv) Power = `("Total work done")/("Time")=12000/25"W"` = 480 W.
संबंधित प्रश्न
A boy weighing 25 kgf climbs up from the first floor at height 3 m above the ground to the third floor at height 9m above the ground. What will be the increase in his gravitational potential energy? (Take g = 10 N kg -1)
Explain by an example that a body may possess energy even when it is not in motion.
A girl weighing 400 N climbs a vertical ladder. If the value of g be 10 m s−2, the work by her after climbing 2 m will be :
A truck driver can load oil drums into the back of the truck by pushing them up a sloping plank, or by lifting them directly. Each drum has a mass of 80 kg, the plank is 3 m long, and the back of the truck is 0.8 m above the ground.
(i) How much force would be needed to lift a drum into the truck directly/without using the plank? (Take g = 10 m/s2)
(ii) How much energy would be required in lifting the drum into the truck without the plank?
(iii) If the force needed to push the drum up the plank is 300 N, why is this less than the answer to part (i)?
(iv) When the truck is loaded, the driver drives off. List the major energy changes that take place in moving the truck.
(v) The driver has to stop at the factory gates. What happens to the kinetic energy of the truck?
Look at the activity below. Reason out whether or not work is done in the light of your understanding of the term ‘work’.
Food grains are getting dried in the sun.
What is power? How do you differentiate kilowatt from kilowatt-hour? The Jog Falls in Karnataka state are nearly 20 m high. 2000 tonnes of waterfalls from it in a minute. Calculate the equivalent power if all this energy can be utilized? (g = 10 m s–2)
