PAK-MED STUDY CORNER MDCAT

▼ MDCAT 2019 Physics - MCQs 141 to 173 ▼

141. Heavy nucleus of atoms go through fission so that they can:

A. absorb high amount of energy

B. absorb low amount of energy

C. increase their binding energy per nucleon

D. reduce their binding energy per nucleon

Correct Answer: D. reduce their binding energy per nucleon

Explanation: In fission of heavy nucleus the atoms are bombarded with a neutron which breaks up the heavier unstable nucleus into smaller particles to reduce the binding energy.

142. For projectile motion in the absence of air resistance:

A. vertical speed is constant

B. horizontal force is constant

C. horizontal acceleration is zero

D. vertical acceleration is zero

Correct Answer: C. horizontal acceleration is zero

Explanation: Only gravitational force acts vertically. No net force horizontally, so F=ma → a=0.

143. For a fixed velocity, when the angle of projection is larger than 45°:

A. Both height and range will be less

B. Both height and range will be more

C. Height less but range more

D. Height more but range less

Correct Answer: D. The height attained will be more but the range is less

Explanation: Height ∝ sin²θ is max at 90°. Range ∝ sin2θ is max at 45°, so >45° reduces range.

144. The wavelength of an EM wave having frequency of 3 kHz will be?

A. 80 km

B. 140 km

C. 100 km

D. 120 km

Correct Answer: C. 100 km

Explanation: v = fλ → λ = 3×10⁸ / 3000 = 1×10⁵ m = 100 km.

145. V = 300 sin (100πt). What is 'f'?

A. 25 Hz

B. 200 Hz

C. 50 Hz

D. 100 Hz

Correct Answer: C. 50 Hz

Explanation: ω = 100π. Since ω = 2πf → 100π = 2πf → f = 50Hz.

146. Micrometer least count 0.01 mm. Correct reading?

A. 0.067 cm

B. 0.0067 mm

C. 0.67 cm

D. 6.70 cm

Correct Answer: C. 0.67 cm

Explanation: 0.01 mm = 0.001 cm. So 3 decimal places in cm.

147. Which shows no work is done?

A. Pushing a car

B. Writing an essay

C. Lifting weights

D. The moon orbiting the earth

Correct Answer: D. The moon orbiting the earth

Explanation: W = Fdcosθ. Centripetal force is perpendicular to motion, so cos90°=0 → W=0.

148. Length of simple pendulum doubled, ratio T_new/T_old = ?

A. 1/√2

B. √2

C. 2

D. 1/2

Correct Answer: B. √2

Explanation: T = 2π√(l/g). If l→2l, T increases by √2.

149. Direction of current through load in full-wave rectifier:

A. Inverts for negative cycle

B. Changes for every cycle

C. Inverts for positive cycle

D. Remains constant

Correct Answer: D. Remains constant

Explanation: D1,D2 conduct on +ve, D3,D4 on -ve cycle, keeping current direction same.

150. k = 5×10⁴ N/m, x = 1.4 mm. Strain energy = ?

A. 4.9×10⁻⁵ J

B. 4.9 J

C. 4.9×10⁻⁵ J

D. 4.9×10⁻² J

Correct Answer: D. 4.9×10⁻² J

Explanation: U = ½kx² = 0.5×5×10⁴×(1.4×10⁻³)² = 0.049 J.

151. Two equal masses 'm' moving towards each other with speed 'v' elastic head-on. Final momentum?

A. -mv

B. mv

C. 2m

D. 0 kg m/s

Correct Answer: D. 0 kg m/s

Explanation: p_total = mv - mv = 0. Momentum conserved.

152. KE = X at 27°C. At 327°C KE becomes?

A. 200X

B. 20X

C. 300X

D. 2X

Correct Answer: D. 2X

Explanation: KE ∝ T in Kelvin. 27°C=300K, 327°C=600K. Doubled.

153. Force doubled, velocity constant. Power?

A. No change

B. Squared

C. Halved

D. Doubled

Correct Answer: D. Doubled

Explanation: P = Fv. F↑2, v constant → P↑2.

154. In Double Slit, fringe spacing increases when:

A. D decreases

B. λ increases

C. Distance to fringe increases

D. d increases

Correct Answer: B. the wavelength of the diffracted rays increases

Explanation: β = λD/d. ↑λ or ↑D or ↓d increases β.

155. Area under load-extension graph = ?

A. Stress

B. Strain energy

C. Young modulus

D. Strain

Correct Answer: B. Strain energy

156. Minimum energy to eject electron = ?

A. Work function

B. Stopping potential

C. Threshold frequency

D. EMF

Correct Answer: A. Work function

157. Unit of magnetic flux density T can be expressed as?

A. N⁻¹A⁻¹m

B. N⁻¹A⁻¹m⁻¹

C. N A⁻¹ m

D. N A⁻¹ m⁻¹

Correct Answer: D. N A⁻¹ m⁻¹

Explanation: B = F/IL → N/(A·m) = N A⁻¹ m⁻¹.

158. % uncertainty length 2%, width 3%. Area = ?

A. 1.5%

B. 5%

C. 6%

D. 1%

Correct Answer: B. 5%

Explanation: For multiplication, add % uncertainties: 2%+3%=5%.

159. Quark composition of a Proton?

A. Two up + one down

B. One up + two strange

C. Two up + one strange

D. Two down + one up

Correct Answer: A. Two up quarks and one down quark

160. Source moving towards observer, observed frequency?

A. f' = f(v/(v-vs))

B. f' = f((v+vo)/v)

C. f' = f((v-vo)/v)

D. f' = f(v/(v+vs))

Correct Answer: A. f' = f(v/(v-vs))

161. Work by centripetal force in circular motion?

A. Reduced

B. Maximum

C. Half

D. Zero

Correct Answer: D. Zero

Explanation: Force ⊥ displacement, so θ=90° → W=0.

162. DC to transformer primary → ?

A. Less emf

B. No emf

C. Equal emf

D. More emf

Correct Answer: B. No emf produced in secondary

Explanation: Transformer needs changing flux. DC is constant.

163. Value and units of Planck constant 'h'?

A. 6.63×10⁻³⁴ Js⁻¹

B. 6.63×10⁻⁴³ Js

C. 6.63×10⁻³⁴ Js

D. 3.63×10⁻³⁴ Js

Correct Answer: C. 6.63×10⁻³⁴ Js

164. Negligible current at op-amp input due to?

A. Low Rin

B. Low Rout

C. High Rout

D. High Rin

Correct Answer: D. High input resistance

165. L=7m, B=0.3T, I=1A parallel to field. Force = ?

A. 2.1 N

B. 0 N

C. 3.1 N

D. 7 N

Correct Answer: B. 0 N

Explanation: F = BILsinθ. θ=0° parallel → sin0=0 → F=0.

166. B=1.8×10⁻⁶ T, I=160A. Max force per unit length?

A. 2.88×10⁻⁴ N/m

B. 2.88×10⁻⁸ N/m

C. 2.88×10⁻² N/m

D. 2.88×10⁻⁶ N/m

Correct Answer: A. 2.88×10⁻⁴ N/m

Explanation: F/L = BIsin90° = 1.8×10⁻⁶×160 = 2.88×10⁻⁴.

167. Rate of change of flux by rotating coil ∝ ?

A. emf produced

B. ΔB

C. Resistance

D. Material

Correct Answer: A. Proportional to the emf produced in it

Explanation: Faraday's Law: emf = -dΦ/dt.

168. E at r, V at r. E→E/4, V = ?

A. V/4

B. V/2

C. 4V

D. 2V

Correct Answer: B. V/2

Explanation: E∝1/r², V∝1/r. If E→E/4, r→2r, so V→V/2.

169. In SHM, acceleration max at?

A. Max displacement

B. Center

C. Mean position

D. Half max

Correct Answer: A. maximum displacement from the mean position

170. Energy of photon f=3.0×10¹⁸ Hz, h=6.63×10⁻³⁴?

A. 19.89×10⁻¹⁸ J

B. 1.89×10⁻¹⁶ J

C. 11.89×10⁻¹⁶ J

D. 19.89×10⁻¹⁶ J

Correct Answer: D. 19.89×10⁻¹⁶ J

Explanation: E=hf = 6.63×10⁻³⁴×3.0×10¹⁸ = 19.89×10⁻¹⁶ J.

171. T₁/₂ = 0.693/λ, λ is?

A. half life

B. wavelength

C. activity

D. decay constant

Correct Answer: D. decay constant

172. Path difference for destructive interference?

A. nλ

B. (n+½)λ

C. 2nλ

D. (2n+1)λ

Correct Answer: B. (n+½)λ

173. d=1.00 mm, D=200 cm. Fringe separation = ?

A. Data incomplete

B. λ needed

C. Cannot calculate

D. β = λD/d

Correct Answer: B. λ needed

Explanation: β = λD/d. Wavelength λ not given in question.