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JAMB Physics Past Questions & Answers - Page 318

1,586.

A load of 20N on a wire of cross-sectional area 8 x 10^-7m², produces an extension of 10m². calculate Young's modulus for the material of the wire if its length is 3m

7.0 x 10¹¹Nm^-2

7.5 x 10¹¹Nm^-2

8.5 x 10¹¹Nm^-2

9.0 x 10¹¹Nm^-2

View answer & explanation

Correct answer is B

Young's modulus = $\frac{F}{A}$ $\div$ $\frac{e}{L}$

= $\frac{20}{8 \times 10^{-7}}$ $\div$ $\frac{10^{-4}}{3}$

= 7.5 x 10¹¹Nm^-2

1,587.

An electric water pump rate 1.5 kW, lifts 200kg of water through a vertical height of 6 meters in 10 seconds. What is the efficiency of the pump? [g = 10ms-2, neglecting air resistance]

90.0%

85.0%

80.0%

65.0%

View answer & explanation

Correct answer is C

Efficiency = output x 100

= $\frac{\frac{200 {\times} 10 {\times} {6}}{10}}{1500}$ x $\frac{100}{1}$

= 80%

1,588.

An object of mass 100g projected vertically upwards from the ground level has a velocity of 20ms^-1 at a height of 10m. calculate its initial kinetic energy at the ground level.[g = 10ms^-2, neglect air resistance]

10 J

20 J

30 J

50 J

View answer & explanation

Correct answer is C

Using, v² = u² - 2gx

(20)² = u²1/2 x 10 x 10

u² = 600(m/s)²

initial K.E = - mu²

= $\frac{1}{2}$ x 600

= 30 J

1,589.

A planet has mass m₁ and is at a distance r, from the sun. A second planet has mass m₂ = 10m₁ and at a distance of r₂ = 2r₁ from the sun. Determine the ratio of the gravitational force experienced by the planets.

1 : 5

2 : 5

3 : 5

4 : 5

View answer & explanation

Correct answer is B

g = $\frac{GM}{R^2}$

$\frac{G_1M_1}{r^2_1}$ = $\frac{G_2M_2}{r^2_2}$

$\frac{G_1M_1}{r^2_1}$ = $\frac{G_2 {\times}10 M_1}{(2r_1)^2}$

$\frac{G_1}{G_2}$ = $\frac{2}{5}$

1,590.

A body of mass 2kg moving vertically upwards has its velocity increased uniformly from 10ms^-1 to 40ms^-1 in 4s. Neglecting air resistance, calculate the upward vertical force acting on the body.[g = 10 ms^-1]

15N

20N

35N

45N

View answer & explanation

Correct answer is C

F = mg + ma

F = 2 [10 + $\frac{(40 - 10)}{4}$ ]

F = 35 N

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