most important science entrance question

most important science entrance question

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1    1.  If a body is in equilibrium under the effect of some non col linear forces, then the minimum number of such forces acting upon the body are-

Answer

Equilibrium is when the sum of forces is 0. In order for 2 forces to accomplish this, they have to be colinear.

For equilibrium: Fnet​=0

For non-collinear forces, the resultant of two forces can balance the 3rd force i.e., (F1​​+F2​​)+F3​​=0

⇒F3​​=−(F1​​+F2​​)

Hence minimum number of non-collinear forces for equilibrium =3.

2.which metal is used to connect solar cell to solar panels

Answer

Due to the highest conductivity of  “silver”  it is used to connect solar cell to solar panel.

3.A heater coil is cut into two equal parts and only one part is used in the heater the heat generated now will be

Answer

Heat generated will be doubled.

4.A bar magnet placed in non-uniform magnetic field experiences

Answer

In a non-uniform magnetic field, bar magnet will experience both torque and force.

5.How much water a pump of 2kw power can raise in one minute to a height of 10m?

Answer

2 kW is equal to 2 x 1000 W (as 1 kW = 1000 W). 

 work = mgh, where m = mass , g=acceleration due to gravity( usually 9.8 or 10 )

 and h= height.

  Power = work/time  work done = m x 10 x 10.

  work done = m x 100 J (joule).  power = J/sec (work/time). 

 2000 = 100m/60 as 1 minute is equal to 60 sec. 

 2000 x 60 = 100m 

 120000/100=m  m=1200 kg  1200 kg = 1200 liter ( here water is being raised so in water 1 kg will be equal to 1 liter)

6.In a simple pendulum mass of bob is m and effecting length is L Work done on the pendulum in one complete oscillation in gravitational field of earth is?

 Answer

It will be zero in complete one oscillation due to gravitational force because displacement of bob will be zero.

7.A body falls freely from a lower and travels a distance of 40m in its last two seconds, the height of the tower is ?

 Answer

Let h = the height of the tower that needs to be determined.

Let t be the time of fall.

Then (t - 2) would be the time to reach the top of the 40 meter mark, and let d be the distance fallen till it reaches the 40 m mark.

Using kinematics, we can write: d = 1/2 g (t-2)^2

And H = 1/2 g t^2

H also = 40 + d

Then: H = 40 + 1/2 g (t-2)^2 = 1/2 g t^2

Expand: 40 +5 (t^2 - 4 t + 4) = 5 t^2

40 + 5 t^2 - 20 t + 20 = 5 t^2

Add like terms: - 20 t = - 60

t = 3 s

(t-2) = 1 second

In one second an object falls 5 m

Then H = 45 m

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