# PRACTICE SET 1 MCQs

#### A rain drop starts falling from a height of 1 km. It falls with continuously decreasing accelerations and attains its constants terminal speed after falling through a height of 500 m. Then the work done by the gravitational force in the first half and the second half of the drop journey are in the ratio----

Since the height of fall, 1 km being very small compared to the radius of earth . We can assume g to remain constant throughout. The workdone (mgx, for x distance moved)is clearly same for both the halves of the rain drop’s journey. Since the drop starts from rest and attains a speed v at the end of the first half of its journey, its average speed during this half is v/2. The speed of the drop during the second half is constant and equal to v throughout . The time of fall of the drop during the first half is therefore greater than the corresponding time during the second half.

#### A stone hange from the free end of a sono meter wire whose vibrating length. When turned to a turning fork is 40 cm when the stone Hngs only mmpresed the water Then relative the dencity of the stone is

Where M == mass of the stone m.g (m-Vp)g =(Vp-Vp)g =Vp(p/p-1)g Nw n== 1/21 √pvg/m From equations (1) and (2) n/n= 1/1 (vP (p/p)-1_g)/m p/p = 16/7

#### An electron in a hydrogen like atom is in an excited state . it has total energy -3-4 eV .its kinetic energy is –

The electrostatic force between electron and the nuclear obeys inverse square obeys inverse square law. There fore its kinetic energy and total energy squae law There fore its energy and total energy are related as

#### A Coolidge tube is operated at 120 KV. The minimum wavelength of x-rays will be

min=hc/eV = x=(6.6*10-34*3*108)/(1.6*10-19*120*103) = 0.1* 10-10 m = 0-1 A°

#### The work function of lithium is 2.3eV.it is exposed to light of wavelength 4.8* 10-7 m The maximum kinetic energy of the emited phoelectrons will be –

Max k.E. = m-Ø m=hc/2 =(6.6*10-34*3*108)/(4.8*10-7*1.6*10-19eV) = (K.E) max2.58-2.3 = 0-28eV

#### 8 Earth receives 1400 w/m2 of solar power . If all the solar energy falling on a lens of aera 0-2 m2 is focused on to a block of ice of mass 280 grams , the time taken taken to melt it will be- (Latent heat of fusion of ice = 3.3 * 105 j/kg)

Energy required to melt = Energy fallen mL= PA* 1 0.280*3.3*105 = 1400*0.2*1 t= 330 sec = 5.5 minutes.

#### An open pipe is suddenly closed at one end with the result that the requency of third harmonic of the closed pipe is found to be higher by The fundamental frequency of the open endpipe is-

The frequency of third harmonic of closed end pipe 3v/41 According to problem 3v/41 = v/21 + 100 = v/41 = 100 = v/21 = 200

#### . If distance between the earth and the sun were halfits present value would have been

According to keeper law ( (T1/T2) = (r1/r2) (365/t2)= (2)3

#### The temperature of 100 gm of water is to e raised from 24°to 90°c by adding steam to it. Calculate the mass of the steam required for this purpose----

Heat is given by steam in condensing (=mL) and by water so formed in coming from 100°c to 90° C. This haet will raise the temperature of 100 gm of steam be required .

#### A person standing with stretched arms on a rotating platform , suddenly pulls down his arms. Then---

From principal of conversation of angular momentum j= iw- const By pulling back hands movement of intertia I will dreases Hence w would increases to keep anguklar momentum j constent.

#### In a straight conducting wire a constant current is following from left to right due to a sources of e.m when the current is switched off the directions of the induced current will be---

When the sources of e.m is switched off induced of productions of this current in this wire. According to Lenz. Law Induced current in the wore Hence the induced current will flow from left to right in the wire.

#### A vessel Of volume 30 litter contains ideals gasd at the temperature 63 ° after a portions of the gas isa let the pressure in the vessel decreases by 0.415 bar . if the dencity of gas at NTP is 1.3 mass of gas released is -----

Share your Results: