HSSC-1 (Class-11) Solved Physics MCQs; Unit-4: Work and Energy;  (New Book/KPK Text Board, Peshawar) With Verified Answers 


1. You push a heavy crate down a ramp at a constant velocity. Only four forces act on the crate. Which force does the greatest magnitude of work on the crate?




... Answer is A. The force of friction
 On a Horizontal Surface only pushing force is responsible for sliding the object and that is greater that the friction. But on the ramp, the combined gravitational force and pushing forces are responsible for sliding the crate down. The normal force does not work. So Friction force is more among all the forces.


2. The force constant of a wire is k and that of another wire is 3k when both the wires are stretched through the same distance, if the work done is W₁ and W₂, then




... Answer is D. W₂ = 3 W₁
Force Constant of one wire let k₁ = k and another wire k₂ = 3k = 3k₁ 👉 Work required = change in energy 👉 W = 𝛥 E = 1/2 kx² 👉 W₁ = 𝛥 E₁ = 1/2 kx² 👉 W₂ = 𝛥 E₂ = 1/2 (3k) x² = 3 (1/2 k x²) = 3 W₁


3. Escape velocity on the surface of the earth is 11.2 km s⁻¹. If the mass of the earth increases to twice its value and the radius of the earth becomes half the escape velocity is




... Answer is C. 22.4 km s⁻¹
Ve = √ (2GMe/Re)= 11.2 km s⁻¹ 👉 When Me with 2 Me and Re with 1/2 Re we get 👉 Ve = √ 4 (2GMe/Re)= 2 √ (2GMe/Re) = 2 (11.2 km s⁻¹) = 22.4 km s⁻¹ 👉 i.e.. The Escape velocity becomes double


4. An example of non-conservative force is:




... Answer is C. Frictional force
The Frictional Force is non-conservative because if an object is moved over a rough surface between two points along different paths. The work done against the frictional force certainly depends on the path followed. Electric and gravitational forces are conservative and magnetic may and may not be conservative depending on some conditions.


5. When the speed of your car is doubled, by what factor does its kinetic energy increase?




... Answer is C. 4
K.E = 1/2 m v² 👉 by replacing v with 2v 👉 K.E = 1/2 m (2v)² = 4 (1/2 m v²) = 4 K.E


6. One horsepower is given by:




... Answer is A. 746 W
In British Engineering System the unit of Power is called Horse Power (hp) and numerically, 1 hp = 746 W (watts)


7. Work is said to be negative when F and d are: :




... Answer is B. Anti Parallel
F and d antiparallel means the angle between them is 180°. Work W is sculler quantity is equal to the dot product of F and d. 👉 W = F • d = F d cos𝜃 = F d cos (180°) = -Fd (negative work)


8. Two bodies of masses m₁ and m₂ have equal momentum their kinetic energies E₁ and E₂ are in the ratio




... Answer is C. m₂ : m₁
 Given: P1 = P2 (given) 👉 K.E = E = 1/2 mv² = m² v² / 2 m = p² /2m 👉 E₁/E₂ = (p₁² /2m₁) / (p₂² /2m₂) 👉 E₁/E₂ = m₂/m₁ E₁ : E₂ = m₂ : m₁


9. The atmosphere is held to the earth by




... Answer is B. Gravity
The atmosphere (gasses) is held to the earth by the earth's gravitational force.


10. If momentum is increased by 20% then K.E increases by




... Answer is A. 44%
K.E = E = 1/2 mv² = m² v² / 2 m = p² /2m 👉 K.E = p² /2m 👉 increase of 20% 👉 Δ K.E = (p + 20% P )² /2m 👉 Δ K.E = (p + (20/100) P )² /2m 👉 Δ K.E = {p² + (400/10000) p² + 40/100 P²)} /2m 👉 by taking p² common Δ K.E =  { 1 + 0.04 + 0.4 )} p²/2m 👉 Δ K.E = 1.44 K.E 👉 Δ K.E - K.E = 1.44 K.E - K.E = .44 K.E = 44 % K.E


11. If the K.E of a body becomes four times of the initial value, then new momentum will




... Answer is A. Become twice its initial value
👉 K.E = p² /2m 👉 P = √ (2m K.E) 👉 by increasing K.E four-time than P' = √ (2m 4 K.E) 👉 P' = 2 √ (2m K.E) = 2 P


12. Two bodies with kinetic energies in the ratio of 4 : 1 are moving with equal linear momentum. The ratio of their masses is :




... Answer is D. 1 : 4
K.E₁ : K.E₂ = 4 : 1 (given) 👉 K.E = E = 1/2 mv² = m² v² / 2 m = p² /2m 👉 K.E₁/K.E₂ = (p₁² /2m₁) / (p₂² /2m₂) 👉 4/1 = m₂/m₁ 👉 by reversing the friction we get m₁/m₂ = 1/4 👉 m₁ : m₂ = 1 : 4


13. A body of mass 5 kg is moving with a momentum of 10 kg m s⁻¹. A force of 0.2 N acts on it in the direction of motion of the body for 10s. The increase in its kinetic energy is




... Answer is D. 36.7
K.E (initial) = p² /2m = (10 kg m s⁻¹)²/2 x 5 kg = 10 J 👉 Now K.E (final) = 1/2 m vf² when a F= 0.2 N at t= 10 s 👉 we have find vf = ? using equation vf = vi + at 👉 from P= mvi 👉 vi =p/m = 10 / 5 = 2 m/s 👉 a = F/m = 0.2/5 = 0.4 m/s² 👉 Now vf = vi + at = 2 m/s + 0.4 m/s² x 10 s = 2.4 m/s 👉 And K.E (final) = 1/2 m vf²​ = 0.5 x g kg x 2.4 m/s = 14.4 J 👉 increase in K.E = K.E (final) - K.E (initial) = 14.4 J - 10 J = 4.4 J ----Ans


14.  If the force and displacement of a particle in the direction of force are doubled. Work would be




... Answer is B. 4 times
W = Fd 👉 if we replace F with 2F and d with 2d then 👉 W' = 2F x 2d = 4 Fd = 4 F


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