JAMB Physics Past Questions & Answers - Page 156

776.

In an inelastic collision

I. Energy is conserved
II. Energy is decreased
III. Energy is increased
IV. Linear momentum conserved

A.

I only

B.

II and IV only

C.

II only

D.

III only

Correct answer is B

In an inelastic collision, linear momentum is conserved and energy is decreased

Momentum and kinetic energy are conserved in elastic collision

777.

Which of the following instrument is most accurately for comparing electromotive force (e.m.f) of two cells?

A.

Voltmeter

B.

Meter rule

C.

Galvanometer

D.

Potentiometer

Correct answer is D

Voltmeter: an instrument for measuring electric potential in volts

Galvanometer: it is a device used to indicate direction of a small electric current

Potentiometer: is a device for measuring or comparing e.m.fs of cells

Meter rule: measuring a distance at different points

778.

When a man moves toward a plane mirror at a speed of 6m/s, the distance the man and his image increased at a speed of?

A.

2 m/s

B.

4 m/s

C.

12 m/s

D.

14 m/s

Correct answer is C

d = y, s = 6 m/s (The Man & Plane Mirror)

d – δy, s = (5 &ndash ;6) m/s (The Man and Image)

d2 ÷ s1 = d2 ÷ s2, y ÷ 6 = 2y ÷ s + 6

Y (s + 6) = 2y × 6

s + 6 = 12

So = 12 – 6 = 6

Since S + 6 = 0

Then, S = 6 (substitute the value of S i.e S = 6)

Into S + 6 = 0

∴So = S + 6 = 6 + 6 = 12 m/s

∴ S = 12 m/s

779.

Volatile liquids usually

A.

Have high boiling points

B.

have low boiling points

C.

have high densities

D.

have high melting points

Correct answer is B

Volatile liquids (i.e. Ammonia or Freon) are usually have low boiling point

780.

Efficiency of a transformer is equal to

A.

Efficiency of transformer = (secondary coil ÷ primary coil) × 100%

B.

Efficiency of transformer = (mechanical advantage ÷ velocity ratio) × 100%

C.

Efficiency of a transformer = (Number of turns in the secondary coil ÷ Number of turns in the primary coil) × 100%

D.

Efficiency of a transformer = (power developed in the secondary coil ÷ power supplied to the primary coil) × 100%

Correct answer is D

Efficiency of a transformer = (power developed in the secondary coil ÷ power supplied to the primary coil) × 100%