Advertisements
Advertisements
प्रश्न
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?
उत्तर
(i) F = mg = 80 × 10 = 800 N.
(ii) Energy = m × g × h = 80 × 10 × 0.8 = 640 J.
(iii) In this case F = mg sin θ = `800xx0.8/3=640/3` = 213.3 N.
It is less than the answer in part (i) as the efforts act through 3 m whereas the weight is lifted up through 0.8 m. The effort needed maybe 300 N instead of 213.3 N owing to loss of energy in overcoming friction and air resistance.
(iv) The energy released owing to the combustion of fuel changes into kinetic energy of the truck and load, and these changes in heat energy of the pebbles on the road and of wheels.
(v) The kinetic energy is dissipated as heat.
APPEARS IN
संबंधित प्रश्न
Name a common device where a gear train is used
Derive a relationship between S.I. and C.C.S. unit of work
Give reasons for the following A teacher moving around in the class is doing work but a child standing and reading a book is not doing any work.
1 J = ______ calorie.
A weight lifter lifted a load of 200 kgf to a height of 2.5 m in 5 s. Calculate:
- the work done, and
- the power developed by him. Take g = 10 N kg-1
A machine raises a load of 750 N through a height of 16 m in 5 s. calculate:
- energy spent by machine,
- power at which the machine works.
A vessel containing 50 kg of water is placed at a height 15 m above the ground. Assuming the gravitational potential energy at ground to be zero, what will be the gravitational potential energy of water in the vessel? (g = 10 m s-2)
A boy throws a rubber ball vertically upwards. What type of work, positive or negative, is done : by the force applied by the boy?
(a) by the force applied by the boy?
(b) by the gravitational force of earth?
A max X goes to the top of a building by a vertical spiral staircase. Another man Y of the same mass goes to the top of the same building by a slanting ladder. Which of the two does more work against gravity and why?
No work is done by a man moving on a horizontal road while carrying a box on his head. Explain.
A cricket ball is thrown up from the earth's surface. What happens to its P.E.
(a) during the motion
(b) at the highest point?
Fill in the boxe to show the corresponding energy transformation.
State the energy changes which take place when A piece of magnesium wire is burnt in a jar of oxygen.
Name the material commonly used for the manufacturing of solar cells.
If a ball is dropped on the sloping roof of a house, it acquires ______ and falls on the ground. That is the transformation of ______ energy into ______ energy takes place.
(kinetic, potential, motion)
