Work done by a force is positive when:
A Force opposes motion
B Force and displacement are in same direction
C Force is perpendicular
D Body is at rest
Positive work occurs when displacement aligns with force.
Work–energy theorem relates work to:
A Change in PE
B Change in KE
C Change in mass
D Change in acceleration
Wnet = ΔKE.
A body’s kinetic energy becomes zero when:
A Net work is positive
B Net work is negative
C Velocity becomes zero
D Mass decreases
KE depends on velocity.
Work done by a constant force depends on:
A Time
B Displacement
C Temperature
D Mass only
W = Fd cosθ.
If work done is zero, then:
A Force is zero
B Displacement is zero or perpendicular
C Body must be at rest
D KE increases
Zero work means either no displacement or ⟂ directions.
A force of 5 N acts through 2 m at 60°. Work =
A 2.5 J
B 5 J
C 10 J
D 20 J
W = Fd cos60° = 5×2×0.5 = 5 J.
KE of a body is 40 J. If speed doubles, KE becomes:
A 80 J
B 160 J
C 20 J
D 100 J
KE ∝ v² → doubling speed = 4×.
Work done by an ideal spring is:
A Positive
B Negative
C Zero
D Can be positive or negative
Depends on compression/expansion direction.
At maximum height of projectile, work done by gravity is:
A Positive
B Zero
C Negative
D Infinite
Gravity acts downward; displacement is upward.
Work done by a variable force is obtained from:
A Area under v–t graph
B Area under F–x graph
C Area under F–t graph
D Area under KE–t graph
W = ∫F dx.
The essential feature of a conservative force is:
A Work depends on path
B Work always increases KE
C Work in closed path is zero
D Work reduces PE
Zero work over closed loops.
Potential energy exists only for:
A Conservative forces
B Non-conservative forces
C Random forces
D Very strong forces
PE is defined for conservative fields.
In presence of friction, mechanical energy:
A Increases
B Decreases
C Remains constant
D Becomes infinite
Friction dissipates energy.
Which force is not conservative?
A Gravity
B Electric force
C Magnetic force
D Friction
Friction depends on path.
Work done by gravitational force:
A Depends on path
B Depends on final height
C Is always zero
D Is always positive
Conservative → only depends on initial/final positions.
A non-conservative force:
A Stores energy
B Converts mechanical energy into heat
C Gives back energy
D Performs no work
Friction dissipates energy.
Work done by spring force from x = 0 to x is:
A +½kx²
B −½kx²
C kx
D Zero
Work done by spring is negative of PE.
If mechanical energy is decreasing, the force involved is:
A Gravity
B Spring force
C Friction
D Electrostatic
Only non-conservative forces reduce ME.
Centre of mass of two particles lies closer to:
A Lighter one
B Heavier one
C Depends on speed
D Always midway
COM is mass-weighted.
COM of a semicircular wire lies:
A At centre
B On diameter
C Outside the arc
D At centre of curvature
Standard COM result.
COM of a moving system is affected only by:
A Internal forces
B External forces
C Both
D Temperature
Internal forces cancel pairwise.
COM of a triangular lamina lies at:
A Centroid
B Vertex
C Midpoint of a side
D Outside the lamina
Geometric centre for uniform density.
If net external force = 0, momentum of system:
A Increases
B Decreases
C Remains constant
D Becomes zero
Linear momentum conserved.
In a collision, COM of system:
A Jumps
B Moves irregularly
C Moves uniformly
D Restarts motion
Internal forces do not affect COM motion.
If two masses 2 kg and 6 kg are 4 m apart, COM measured from 2 kg is:
A 1 m
B 2 m
C 3 m
D 4 m
COM closer to heavier mass: x = (6/8)×4 = 3.
COM can be outside body in:
A Solid cube
B Ring
C Sphere
D Cylinder
Ring’s COM lies at geometric centre (empty).
Momentum is conserved in:
A Any motion
B Systems with external forces
C Absence of external forces
D Rotational motion only
No external force → momentum constant.
A 5 kg mass moving at 2 m/s has momentum:
A 5
B 10
C 2
D 7
p = mv.
Impulse equals:
A Change in KE
B Change in PE
C Change in momentum
D Change in power
J = Δp.
Perfectly elastic collision conserves:
A KE only
B Momentum only
C Both KE & momentum
D Neither
Elastic collision → both conserved.
A bullet embeds in a block. This is:
A Elastic
B Perfectly inelastic
C Explosion
D Oblique collision
Bodies stick.
Unit of momentum is:
A Joule
B Watt
C Newton
D kg·m/s
From p = mv.
Force equals rate of change of:
A KE
B Power
C Displacement
D Momentum
Newton’s second law.
A 3 kg body experiences impulse 9 Ns. Change in velocity =
A 1 m/s
B 2 m/s
C 3 m/s
D 4 m/s
Δv = J/m = 9/3 = 3.
When two bodies collide, momentum is conserved if:
A Forces are equal
B No external force acts
C Bodies have equal mass
D KE decreases
Condition for momentum conservation.
Total mechanical energy of system is conserved when:
A Only friction acts
B Only conservative forces act
C External force acts
D Mass increases
No dissipation.
A falling body’s KE increases because:
A Air resistance helps
B PE converts to KE
C Mass increases
D Time increases
Energy transformation.
Energy cannot be created/destroyed is:
A Newton’s law
B Kepler’s law
C Conservation of energy
D Work–energy theorem
Fundamental principle.
Compressed spring stores energy as:
A KE
B Thermal energy
C Chemical energy
D Elastic PE
Given by ½kx².
When velocity triples, KE becomes:
A 3×
B 6×
C 9×
D 12×
KE ∝ v².
Work done by uniform gravity from h₁ to h₂ is:
A mgh₂
B mg(h₂−h₁)
C ½mg(h₂−h₁)
D Zero
Depends only on height difference.
Power =
A Work × time
B Work ÷ time
C Mass ÷ time
D Force × time
Rate of doing work.
If W = 100 J in 2 s, power =
A 25 W
B 50 W
C 75 W
D 100 W
P = 100/2 = 50 W.
Work = 0 when displacement is:
A Parallel
B Opposite
C Perpendicular
D Same direction
Force ⟂ displacement.
KE = ½mv² indicates KE depends on:
A Only mass
B Only velocity
C Mass and square of velocity
D Force
Velocity has stronger effect.
A 4 kg body moving at 3 m/s has KE =
A 6 J
B 18 J
C 36 J
D 9 J
½(4)(9) = 18 J.
If ME is constant, forces acting are:
A Non-conservative
B Always zero
C Conservative
D Internal
ME conserved only for conservative forces.
A force produces no change in KE when:
A Work = 0
B Mass decreases
C Friction acts
D Speed decreases
ΔKE = work done.
A body moves in a circle. Work done by centripetal force:
A Positive
B Negative
C Zero
D Infinite
Perpendicular to motion.
Net external force = 0 implies:
A KE constant
B Momentum constant
C Position constant
D Energy increases
Momentum conserved in isolated system.