Why is electrical power required at all when the elevator is descending? Why should there be a limit on the number of passengers in this case?
Why is electrical power required at all when the elevator is descending? Why should there be a limit on the number of passengers in this case?
This is a short answer type question as classified in NCERT Exemplar
When the elevator is descending then electric power is required to prevent it from falling freely under gravity.
Also as the weight inside the elevator increases, its speed of descending increases, therefore there should be a limit o
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Using Newton’s formula,
This is a multiple choice answer as classified in NCERT Exemplar
This is a multiple choice answer as classified in NCERT Exemplar
(b) conserving energy between “O” ans ”A”

Ui + Ki = Uf + Kf
0+1/2mv2= mgh + 1/2mv’
(v’)2=v2-2gh = v’= ……….1
Let speed after emerging be v1 then
=1/2mv12=1/2[1/2mv’2]
1/2m(v1)2=1/4m(v’)2=1/4m[v2-2gh]
V1= ………….2
From eqn 1 and 2
So v1 = v’/
This is a multiple choice answer as classified in NCERT Exemplar
(b, d) When a man of mass m climbs up the staircases of height L, work done by the gravitational force on the man is mgl work done by internal muscular forces will be mgL as the change in kinetic is almost zero.
Hence total work done =-
This is a multiple choice answer as classified in NCERT Exemplar
(c) m =150g =3/20kg
Time of contact =0.001s
U=126km/h=
V= -35m/s
Change in momentum of the ball = m (v-u)=
=21/2
F= dp/dt=- = - 1.05
Here – negative sign indicates that force will be opposite to the direction of movement of the ball be
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Physics NCERT Exemplar Solutions Class 11th Chapter Six 2025
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