#neet
- The speed of a swimmer in still water is 20 m/s. The speed of river water is 10 m/s and is flowing due east. If he is standing on the south bank and wishes to cross the river along the shortest path, the angle at which he should make his strokes w.r.… Answer: 1. 30^° west To cross along the shortest path (straight north), the swimmer's velocity component along the river flow must cancel th... 1
- A particle moving with velocity V is acted by three forces shown by the vector triangle PQR. The velocity of the particle will : Answer: 3. remain constant In the figure the three vectors overrightarrowPQ,overrightarrowQR,overrightarrowRP are placed head to tail and fo... 1
- Two particles A and B are moving in uniform circular motion in concentric circles of radii r_A and r_B with speed v_A and v_B respectively. Their time period of rotation is the same. The ratio of angular speed of A to that of B will be : Answer: 4. 1 : 1 Angular speed ω=2π/T . Both particles have the same period T , so they have the same angular speed. ω_A:ω_B=1:1 . (Their li... 1
- A block of mass 10 kg is in contact against the inner wall of a hollow cylindrical drum of radius 1 m. The coefficient of friction between the block and the inner wall of the cylinder is 0.1. The minimum angular velocity needed for the cylinder to ke… Answer: 3. 10 rad/s The wall's normal force supplies the centripetal force: N=mω²r . Friction balances weight: μ N=mg . μ mω²r=mg⇒ω=√(g/μ r)... 1
- Two parallel infinite line charges with linear charge densities +λ C/m and -λ C/m are placed at a distance of 2R in free space. What is the electric field mid-way between the two line charges ? Answer: 3. λ/πε₀ R N/C The field of an infinite line charge at distance r is E=λ/2πε₀r . Midway, r=R for each line. The + λ line pushes away... 1
- Two point charges A and B, having charges +Q and -Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes : Answer: 2. 9F/16 25% of A's charge is 0.25Q . After transfer: q_A=0.75Q and q_B=-Q+0.25Q=-0.75Q . Coulomb force F∝ q_Aq_B at the same distan... 1
- A small hole of area of cross-section 2 mm^2 is present near the bottom of a fully filled open tank of height 2 m. Taking g = 10 m/s^2, the rate of flow of water through the open hole would be nearly : Answer: 1. 12.6×10⁻⁶ m ³ /s By Torricelli's theorem the speed of efflux is v=√(2gh) . v=√(2×10×2)=√(40)≈6.32 m/s. Rate of flow =Av=2×10⁻⁶×6.... 1
- Which colour of the light has the longest wavelength ? Answer: 1. red In the visible spectrum wavelength decreases from red to violet (about 700 nm for red, 400 nm for violet). So red has the lon... 1
- Which of the following animals does not undergo metamorphosis ? Answer: 1. Earthworm Key idea: Metamorphosis is a change from larva to adult. Moths (caterpillar), tunicates (tadpole-like larva) and starfi... 1
- Which of the following organisms are known as chief producers in the oceans ? Answer: 3. Diatoms Key idea: Diatoms are the chief producers in the oceans. These are abundant photosynthetic protists (golden-brown algae)... 1
- When a block of mass M is suspended by a long wire of length L, the length of the wire becomes (L+l). The elastic potential energy stored in the extended wire is : Answer: 3. 1/2Mgl The energy stored in a stretched wire equals the work done by the stretching force, which grows linearly from 0 to Mg . U=... 1
- A mass m is attached to a thin wire and whirled in a vertical circle. The wire is most likely to break when : Answer: 3. the mass is at the lowest point The wire breaks where its tension is largest. At the lowest point: T-mg=mv²/r , so T=mg+mv²/r . H... 1
- Ionized hydrogen atoms and α-particles with same momenta enters perpendicular to a constant magnetic field, B. The ratio of their radii of their paths r_H : r_α will be : Answer: 1. 2 : 1 In a magnetic field a charged particle moves in a circle of radius r=p/qB . Momentum p and B are the same, so r∝ 1/q . Ioni... 1
- Body A of mass 4m moving with speed u collides with another body B of mass 2m, at rest. The collision is head on and elastic in nature. After the collision the fraction of energy lost by the colliding body A is : Answer: 2. 8/9 Use the formula for the final speed of a body in a head-on elastic collision with a body at rest. v_A=m₁-m₂/m₁+m₂u=4m-2m/4m+2... 1
- In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away, was found to be 0.2^°. What will be the angular width of the first minima, if the entire experimental app… Answer: 2. 0.15^° For the first minimum, sinθ=λ/d . The angle is small, so θ∝λ . In water, λ'=λ/μ=3/4λ . θ'=3/4×0.2^°=0.15^° . 1
- In which of the following devices, the eddy current effect is not used ? Answer: 3. electromagnet or 4. electric heater Eddy currents are induced in a conductor by a changing magnetic flux. Induction furnace: eddy... 1
- A soap bubble, having radius of 1 mm, is blown from a detergent solution having a surface tension of 2.5×10^-2 N/m. The pressure inside the bubble equals at a point Z_0 below the free surface of water in a container. Taking g = 10 m/s^2, density of w… Answer: 3. 1 cm A soap bubble has two surfaces, so the excess pressure inside is Δ P=4T/R . Δ P=dfrac4×2.5×10⁻²10⁻³=100\ Pa . At depth Z₀ in... 1
- A disc of radius 2 m and mass 100 kg rolls on a horizontal floor. Its centre of mass has speed of 20 cm/s. How much work is needed to stop it ? Answer: 1. 3 J To stop the disc we must remove its total kinetic energy, which is translational plus rotational. K=1/2mv²+1/2Iω² with I=1/2m... 1
- Nissl bodies are mainly composed of Answer: 4. Free ribosomes and RER Key idea: Nissl bodies are granular masses in the cell body and dendrites of neurons. They are made of fre... 1
- All of the following are part of an operon except Answer: 2. an enhancer Key idea: A prokaryotic operon has structural genes, a promoter and an operator (and a regulatory gene nearby). An en... 1
- Hormones secreted by the placenta to maintain pregnancy are Answer: 2. hCG, hPL, progestogens, estrogens Key idea: The placenta works as a temporary endocrine gland. It secretes hCG, hPL (human placen... 1
- The contraceptive 'SAHELI' Answer: 1. blocks estrogen receptors in the uterus, preventing eggs from getting implanted. Key idea: Saheli is a non-steroidal oral contrac... 1
- The amnion of mammalian embryo is derived from Answer: 1. ectoderm and mesoderm Key idea: The extra-embryonic membranes are formed from the germ layers. The amnion is made of extra-embryo... 1
- The difference between spermiogenesis and spermiation is Answer: 4. In spermiogenesis spermatozoa are formed, while in spermiation spermatozoa are released from sertoli cells into the cavity of sem... 1