Forces in Equilibrium

Question 1

An object is in equilibrium when the resultant force on it is:

Accepted Answer

Zero — Equilibrium requires the resultant force to be zero.

Question 2

Which state is NOT possible for an object in equilibrium?

Accepted Answer

Accelerating — Acceleration requires a non-zero resultant force, so it cannot occur in equilibrium.

Question 3

A 4 kg object hangs at rest from a rope (g = 10 m s⁻²). The tension in the rope is:

Accepted Answer

40 N — Tension balances weight: T = mg = 4 × 10 = 40 N.

Question 4

Three forces keeping an object in equilibrium can be drawn as a:

Accepted Answer

Closed triangle — Three balanced forces drawn head-to-tail form a closed triangle of forces.

Question 5

A box on a floor has weight 60 N. In equilibrium, the normal reaction from the floor is:

Accepted Answer

60 N — The normal reaction balances the weight, so R = 60 N.

Question 6

For a body in equilibrium, which pair of conditions must both hold?

Accepted Answer

ΣFx = 0 and ΣFy = 0 — The sum of horizontal and the sum of vertical forces must each be zero.

Question 7

A parachutist falls at constant velocity. The air resistance compared to the weight is:

Accepted Answer

Equal to the weight — Constant velocity means equilibrium, so air resistance equals weight.

Question 8

Two ropes share the weight of a 10 kg sign equally (g = 10 m s⁻²). Each rope's vertical support is:

Accepted Answer

50 N — Total upward force = 100 N; shared equally gives 50 N each.

Question 9

A book rests on a table. The forces on the book are balanced by Newton's:

Accepted Answer

First law — Newton's first law describes a body in equilibrium remaining at rest.

Question 10

A crate is pushed right with 25 N and friction acts left. If the crate moves at constant velocity, the friction is:

Accepted Answer

25 N — Constant velocity means equilibrium, so friction equals the applied force = 25 N.