a body is pulled through a distance of 500m by a force of 20N. if the power developed is 0.4KW, calculate the time for which the force act?

25000N

Explanation:

distance travelled(d)=500m

force(f)=20N

Power=0.4KW=0.4×1000Watt=400watt

Then,Time(T)=?

Now,

Power(P)=W/T

400=F×D/T.(w=f×d)

or, 400=20×500/T

or, 400=10000/T

or, T=10000/400

or,T=25 sec

Therefore,time taken=25 sec

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

according to jean piaget, in what stage of cognitive development are children able to understand conservation task?

b. preoperational

just took it