JAMB Physics Past Questions & Answers - Page 399

1,991.

A reservoir 500 m deep is filled with a fluid of density 850 kgm-3. If the atmospheric pressure is 1.05 x 105 Nm-2, the pressure at the bottom of the reservoir is.

[g = 10ms-2]

A.

4.72 x 106 Nm-2

B.

4.36 x 106 Nm-2

C.

4.28 x 106 Nm-2

D.

4.25 x 106 Nm-2

Correct answer is D

In general, pressure varies with depth in the relation p = lgh
= 850 x 10 x 500
= 4250000
= 4.25 x 106 NM-2

1,992.

A machine has a velocity ratio of 4. if it requires 800 N to overcome a load of 1600 N,what is the efficiency of the machine?

A.

60%

B.

50%

C.

40%

D.

2%

Correct answer is B

Efficiency = (M.A)/V.R X (100)/1
But M.A = (Load)/Effort = (1600)/800 = 2
Efficiency = (2)/4 x (100)/1 = 50%

1,993.

Two spheres of masses 5.0 kg and 10.0 kg are 0.3 m apart. Calculate the force of attraction between them?

[G = 6.67 X 10-11 Nm2 Kg2]

A.

3.50 x 10-10N

B.

3.71 x 10-8 N

C.

3.57 x 10-2N

D.

4.00 x 102N

Correct answer is B

The force of attraction between the two spheres is given by F (GM1 M2)/r2 = (6.67X 10-11 X5X10)/(0.3)2
= 3.71 X 10-8N.

1,994.

A car of mass 1500 kg goes round a circular curve of radius 50m at a speed of 40 ms-1. The magnitude of the centripetal force on the car is ?

A.

4.8 x 104 N

B.

4.8 x 103 N

C.

1.2 x 103 N

D.

1.2 x 102 N

Correct answer is A

Centipetal force of the car = ma = (MV)2/r
= (1500 x 40 x40)/50
= 48000 = 4.8 x 104 N

1,995.

A gramophone record takes 5s to reach its constant angular velocity of 4\(\pi\) rads-1 from rest. Find its constant angular acceleration.

A.

0.4\(\pi\) rads-2

B.

0.8\(\pi\) rads-2

C.

1.3\(\pi\) rads-2

D.

20.0\(\pi\) rads-2

Correct answer is B

From the radiation:
V = +at, and if it starts from N & T, U = 0
And for angular motion, W = O + at
4R = aχ5
∴ a = (4a)/5 = 0. 8\(\pi\) rads-2