JAMB Physics Past Questions & Answers - Page 393

1,961.

If a body mass 5kg is thrown vertically upwards with velocity u,at what height will the potential energy equal to the kinetic energy?

A.

h =(u)2/g

B.

h = (u)2/4g

C.

h = (2u)2/g

D.

h = (u)2/2g

Correct answer is B

From V2 = U2 + 2as
O = U 2 - 2gH, since at maximum height H, the final velocity, v = O.

when K.E = P.E
∴ H = (U)2/2g
Halfway is the height / 2

PE = KE at (1)/2 H = (U)2 /2g x (1/2) = U2 / 4g

1,962.

What is the frequency of vibration if the balance wheel of a wrist watch makes 90 revolutions in 25 s?

A.

0.01 Hz

B.

0.04 Hz

C.

2.27 Hz

D.

3.60 Hz

Correct answer is D

Frequency = (No. of revolutions)/ Time = (90)/25 = 3.6 Hz

1,963.

I. All the three forces must be concurrent.
II. The upward force is equal to the downward force.
III. The algebraic sum of the moment about any point must be zero.

which of the above conditions must hold for a body acted upon by a system of three coplanar forces equilibrium?

A.

I and II only

B.

I and III only

C.

II and III only

D.

I, II and II only

Correct answer is D

The condition (ii) is a condition for an equilibrium of parallel forces only while conditions (i) and (iii) are correct for both parallel and non- parallel coplanar forces.

No specifications are made, so all conditions apply.

1,964.

If a wheel 1.2 m in diameter rotates at one revolution per second, calculate the velocity of the wheel.

A.

3.6 ms-1

B.

3.77 ms-1

C.

4.0 ms-1

D.

7.5 ms-1

Correct answer is B

V = wr = 2πf r = 2 x (22)/7 x 1 x 0.6
= 3.77ms-1

1,965.

Which of the following is NOT a vector quantity?

A.

altitude

B.

acceleration

C.

displacement

D.

weight

Correct answer is A

Altitude is just a measure of height, regardless of direction.