2025 - JAMB Physics Past Questions and Answers - page 3

Pressure is defined as the force acting per unit area, expressed mathematically as \( P = \frac{F}{A} \).
The area of the base of the reservoir is found by multiplying the length and breadth. This gives \( A = 10 \times 5 = 50 \, \text{m}^2 \).
The force acting on the base is the weight of the water, which is given as 5000N.
Substituting these values into the pressure formula gives \( P = \frac{5000}{50} \).
Carrying out the division gives \( P = 100 \, \text{N/m}^2 \).
Since \( \text{N/m}^2 \) is the same as Pascal, the pressure is 100Pa.
Therefore, the pressure exerted at the bottom is 100Pa.

The acceleration of a body is determined using Newton’s second law, which states that the net force acting on a body equals mass multiplied by acceleration.
The weight of the body is given by mass multiplied by gravitational acceleration. With mass equal to 10kg and gravitational acceleration equal to 10m/s\(^2\), the weight becomes \( 10 \times 10 = 100 \, \text{N} \).
The upward forces opposing the motion are the upthrust of 10N and the viscous drag of 15N. Their total is \( 10 + 15 = 25 \, \text{N} \).
The net downward force is therefore the difference between the weight and the upward forces, which gives \( 100 - 25 = 75 \, \text{N} \).
Using Newton’s second law, acceleration is obtained by dividing the net force by the mass. This gives \( a = \frac{75}{10} \).
Evaluating this gives \( a = 7.5 \, \text{m/s}^2 \).
Therefore, the acceleration of the body is 7.5m/s\(^2\).

The force on a moving charge in a magnetic field is given by \( F = qvB\sin\theta \).
Rearranging this formula to make the magnetic flux density the subject gives \( B = \frac{F}{qv\sin\theta} \).
The charge is \( 5 \times 10^{-6} \, \text{C} \), the speed is \( 3 \times 10^4 \, \text{m/s} \), and the angle is 45º. The sine of 45º is \( \frac{\sqrt{2}}{2} \).
Substituting these values gives \( B = \frac{6}{(5 \times 10^{-6})(3 \times 10^4)\left(\frac{\sqrt{2}}{2}\right)} \).
Multiplying the charge and velocity gives \( 15 \times 10^{-2} = 0.15 \).
Multiplying this by \( \frac{\sqrt{2}}{2} \approx 0.707 \) gives approximately 0.106.
Dividing 6 by 0.106 gives approximately 56.6T.
Therefore, the magnetic flux density is about 56.57T.

Electrical energy in kilowatt-hours is calculated by multiplying power in kilowatts by time in hours.
The given power is 150W, which is equal to \( \frac{150}{1000} = 0.15 \, \text{kW} \).
The time of operation is 336 hours.
Multiplying power by time gives \( 0.15 \times 336 \).
This gives \( 50.4 \, \text{kWh} \).
Therefore, the total electrical energy consumed is 50.40kWh.

Distance travelled by sound is calculated using the relation distance equals speed multiplied by time.
The speed of sound is given as 60m/s and the time delay is 4 seconds.
Multiplying these gives \( 60 \times 4 = 240 \, \text{m} \).
This means the sound travelled 240 metres from the storm to the observer.
Therefore, the observer is 240m from the centre of the storm.

The heat required is calculated using the expression \( Q = mc\Delta T \).
The mass is 4kg, the specific heat capacity is 4200J/kgK, and the temperature increase is \( 65 - 30 = 35K \).
Substituting gives \( Q = 4 \times 4200 \times 35 \).
This gives \( Q = 588000 \, \text{J} \).
The electrical power supplied is given by multiplying voltage and current. This gives \( P = 240 \times 5 = 1200 \, \text{W} \).
Time is obtained by dividing energy by power. This gives \( t = \frac{588000}{1200} \).
Evaluating this gives 490 seconds.
Therefore, the heating time required is 490s.

When water vapour condenses around tiny particles such as dust, it forms very small liquid droplets.
If these droplets remain suspended close to the Earth's surface, they reduce visibility and create a thick, cloudy condition near the ground.
This ground-level suspension of condensed droplets is known as fog.
Therefore, the correct answer is fog.

The horizontal forces act in opposite directions, so the net horizontal force is obtained by subtracting the smaller force from the larger one. This gives \( 8 - 4 = 4 \, \text{N} \).
The vertical forces also oppose each other, so the net vertical force is \( 15 - 12 = 3 \, \text{N} \).
The resultant force is found using Pythagoras' theorem since the horizontal and vertical components are perpendicular.
This gives \( R = \sqrt{4^2 + 3^2} \).
Squaring the values gives 16 and 9, and their sum is 25.
The square root of 25 is 5.
Therefore, the resultant force has magnitude 5N.

The eye focuses on objects at different distances by changing the curvature of its lens.
This change in shape is controlled by a ring of muscles attached to the lens.
When these muscles contract or relax, they alter the thickness of the lens, which changes its focal length.
These muscles are known as the ciliary muscles.
Therefore, the focal length of the eye lens is varied by the ciliary muscle.

Electrical power is related to current and voltage by the formula \( P = VI \).
To find the current, the formula is rearranged to give \( I = \frac{P}{V} \).
The power is given as 500W and the voltage is 220V.
Substituting these values gives \( I = \frac{500}{220} \).
Dividing 500 by 220 gives approximately 2.27.
Therefore, the current drawn by the oven is 2.27A.