Physics(Exams > Bitsat ) Questions and answers for exam Preparation

Exams > Bitsat

PHYSICS MCQs

Total Questions : 421 | Page 4 of 43 pages

Question 31.

which of the following has centre of mass no situated in the material of body ?

A rod bent in the from of circle
Football
Handring
All of above

Discuss Question

Answer: Option D. -> All of above

(A) If a rid is bent in the form of a circle . Its centre of mass is at the centre of curvature

(B) Football is in the shape of hollow sphere So, its centre of mass is at the centre of sphere

In all the above geometrical shape , no material is present at the centre of mass

Question 32.

Centre of mass of a semicircular plate of radius R , the density of which linearly varies with distance , d at centre to a value 2d at circumference is

3R/`pi` from certre
4R/2`pi` from certre
5R/`pi` from certre
7R/5`pi` from certre

Discuss Question

Answer: Option D. -> 7R/5`pi` from certre

Question 33.

Mark correct or options

Nagpur can be said to the geographical centre of india
The population centre of india may be Uttar Pradesh
The population centre may be coincided with geographical centre
All the above

Discuss Question

Answer: Option D. -> All the above

Question 34.

A particle move with a velocity `(5 hat(i) - 3 hat(j) + 6 hat (k))` m/s under the influence of a constant force

`vec(F) = 10 hat(i) + 10 hat(j) + 20 hat(k)`. The instantaneous power applied to the particle is

200 j /sec
40 j /sec
140 j /sec
170 j /sec

Discuss Question

Answer: Option C. -> 140 j /sec

`because vec(v) = (5 hat(i) - 3hat(j) + 6 hat(k)` m/s

`vec (F) = 10 hat(i) + 10 hat(j) + 20 hat(k)`

`:.` power =` vec(F) * vec (v)`

= `(10hat(i) + 10 hat (j) + 20 hat (k)) * (5hat(i) - 3hat(j) + 6 hat(k))`

= 50 - 30 + 120 = 140 joule / sec

Question 35.

A wind powered generator converts wind energy into electrical energy . Assume that the generator converts a fixed fraction of the wind energy intercepted by its blades into electrical energy for wind speed v the electrical power output will be proportional to

v
`v^2`
`v^3`
`v^4`

Discuss Question

Answer: Option C. -> `v^3`

Question 36.

A particle of mass m is moving in a circular path of constant radius r such that its centripetal acceleration `a_c` is varying with time t as `a_c = k^2 r t^2`. The power is

`2 pi mk^2r^2 t`
`mk^2 r^2t`
`(mk^4 r^2 t^5)/(3)`
zero

Discuss Question

Answer: Option B. -> `mk^2 r^2t`

`a_c = v^2/r = k^2 r t^2`

`because v = krt`

The tangential accelerationis

`a_1 = (dv)/(dt) = (d(rt))/(dt) = kr`

The work done by centripetal force will be zero.

so , power is delivered to the particle by only tangential force which acts in he same direction of instantaneous velocity .

`:.` power = `F_1 v`

= `ma_1 krt`

= `m(kr) (krt) = mk^2 r^2 t`

Question 37.

The power supplied by a force acting on a particle moving in a straight line is constant . The velocity of the particle varies with the displacement `x` as

`sqrt(x)`
`x`
`x^2`
`x^(1/3)`

Discuss Question

Answer: Option D. -> `x^(1/3)`

(D) `because ` p = Fv = (ma) v = `m((d^2 x)/(dt^2)) ((dx)/(dt))`

Since , power is constant ,

`:.` ` ((d^2 x)/(dt^2)) ((dx)/(dt))` = k

or `((d)/(dt)) ((dx)/(dt))^2 = k`

or `((dx)/(dt))^2 = k_1` t

or ` (dx)/(dt) = sqrt(k_1 t) = k _2 t^(1/2)`

or ` x = k_3 t^(3/2)`

Hence `(dx)/(dt) prop t^(1/2) prop x^(1/3)`

Question 38.

A man weighing 60 kg climbs a staircase carrying a 20 g load on his hand . The staircase has 20 steps and each step has a height of 20 cm . It he takes 20 second to climb , his power is

160 w
230 w
320 w
80 w

Discuss Question

Answer: Option A. -> 160 w

Power = `((60 + 20) xx (10) xx (20 xx 0.2))/(20)` = 160 w

Question 39.

The average human heart force four time lire of blood per minute through arteries a pressure of 125 mm . If the density of blood `1.03 xx 10^3 kg ` /`m^3`. Then the power of heart is

112.76 x `10^-6` HP
112.76 HP
1.03 x`10^3` HP
1.03 x` 10^-6` HP

Discuss Question

Answer: Option A. -> 112.76 x `10^-6` HP

Question 40.

An object of mass M , initially at rest under the action of a constant force F attains a velocity v in time t Then the average power supplied to the mass is