Advertisements
Advertisements
प्रश्न
A man squatting on the ground gets straight up and stand. The force of reaction of ground on the man during the process is ______.
विकल्प
constant and equal to mg in magnitude.
constant and greater than mg in magnitude.
variable but always greater than mg.
at first greater than mg, and later becomes equal to mg.
Advertisements
उत्तर
A man squatting on the ground gets straight up and stand. The force of reaction of ground on the man during the process is at first greater than mg, and later becomes equal to mg.
Explanation:
When the man is squatting on the ground he is tilted somewhat, hence he also has to balance frictional force besides his weight in this case.
R = reactional force = friction + mg
⇒ R > mg
When the man gets straight up in that case friction ≈ 0
⇒ Reactional force ≈ mg
APPEARS IN
संबंधित प्रश्न
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Work done = Force × ........................................
1 J = ______ calorie.
State two advantage of producing hydroelectricity.
What do you mean by degradation of energy?
State the SI unit of work.
What is meant by a translational motion? Give one example.
Draw a neat labeled diagram to show the direction of two forces acting on a body to produce rotation in it. Also mark the point about which rotation takes place.
P, Q and R are three forces which act as shown in fig.
The point O lies in the same plane. Given, P = Q = R = 10N
(i) Which force has the least moment about O? Give a reason.
(ii)Which force has the greatest moment about O? Give a reason.
Is work done a scalar or a vector physical quantity?
When you move upstairs, do you perform some work?
No work is done by a man moving on a horizontal road while carrying a box on his head. Explain.
Fill in the boxe to show the corresponding energy transformation.
State the energy changes which take place when A toy car with a wound spring moves on ground.
State the amount of work done by an object when it moves in a circular path for one complete rotation. Give a reason to justify your answer.
A block of mass 30 kg is pulled up a slope, as shown in diagram with a constant speed, by applying a force of 200 N parallel to slope.
A and B are initial and final positions of block.
(i) Calculate the work done by force in moving the block from A to B.
(ii) Calculate P.E. gained by block. [g=10ms-2]
A force is applied on a body of mass 20 kg moving with a velocity of 40 ms−1. The body attains a velocity of 50 ms−1 in 2 seconds. Calculate the work done by the body.
How long should an electric motor, of power 2 H.P. operate, so as to pump 5 m3 of water from a depth of 15m. [Take g = 10 N kg−1]
Look at the activity below. Reason out whether or not work is done in the light of your understanding of the term ‘work’.
A green plant is carrying out photosynthesis.
