Pressure
What is the formula for pressure, and what are the SI units of pressure?
Pressure = Force ÷ Area. The SI unit is Pascal (Pa), where 1 Pa = 1 N/m².
What is a moment in physics, and what is its formula?
A moment is the turning effect of a force about a pivot.
Formula: Moment = Force × Perpendicular Distance from the pivot
SI unit: Newton meter (Nm)
What is the difference between speed and velocity?
Speed is the rate at which an object moves (scalar – no direction).
Velocity is speed with direction (vector).
Example: 10 m/s (speed), 10 m/s east (velocity).
What is energy, and what is its SI unit?
Energy is the ability to do work or cause change. The SI unit of energy is the joule (J).
A force of 100 N is applied to a surface area of 2 m². What is the pressure exerted on the surface?
Pressure = 100 N ÷ 2 m² = 50 Pa
A force of 10 N is applied at a distance of 0.5 m from a pivot. What is the moment produced?
Moment = 10 N × 0.5 m = 5 Nm
A car travels 100 meters in 20 seconds. What is its average speed?
Speed = Distance ÷ Time = 100 m ÷ 20 s = 5 m/s
How much work is done if a force of 10 N moves an object 3 meters in the direction of the force?
Work = Force × Distance = 10 N × 3 m = 30 J
A woman wearing high heels exerts more pressure on the ground than an elephant. Why?
Because the area of the heel is very small, and pressure is inversely proportional to area (P = F/A), even a small force over a small area creates high pressure.
Why is it easier to open a door by pushing at the edge farthest from the hinge than near the hinge?
Because the distance from the pivot is greater at the edge, so for the same force, the moment is larger, making it easier to turn the door.
A car starts from rest and accelerates at 2 m/s² for 6 seconds. What is its final velocity?
Use: v = u + at
u = 0, a = 2, t = 6
v = 0 + 2 × 6 = 12 m/s
A 2 kg object is lifted to a height of 5 meters. What is its gravitational potential energy? (Take g = 10 m/s²)
GPE = mgh = 2 × 10 × 5 = 100 J
Calculate the pressure at a depth of 5 m in water. (Density of water = 1000 kg/m³, g = 9.8 m/s²)
Pressure = ρgh = 1000 × 9.8 × 5 = 49,000 Pa
A uniform beam is balanced on a pivot. A 30 N weight is placed 2 m to the left of the pivot. Where should a 20 N weight be placed on the right side to keep it balanced?
Clockwise moment = Anticlockwise moment
20 N × x = 30 N × 2 m → 20x = 60 → x = 3 m
A cyclist accelerates from 5 m/s to 15 m/s in 4 seconds. What is the displacement during this time?
Use: s = ((u + v)/2) × t
s = ((5 + 15)/2) × 4 = (20/2) × 4 = 10 × 4 = 40 m
What is the kinetic energy of a 4 kg object moving at 3 m/s?
KE = ½mv² = ½ × 4 × (3)² = 2 × 9 = 18 J
A hydraulic press has a small piston of area 0.01 m² and a large piston of area 1 m². If a force of 200 N is applied to the small piston, what force is exerted by the large piston (assuming no energy loss)?
Pressure on small piston = 200 N ÷ 0.01 m² = 20,000 Pa
Since pressure is transmitted equally:
Force on large piston = Pressure × Area = 20,000 Pa × 1 m² = 20,000 N
A see-saw is 4 meters long and balanced at the center. A child of mass 40 kg sits 1.5 m from one end. Where must a second child of mass 30 kg sit on the other side to balance the see-saw? (Take g = 10 m/s²)
Weight of child 1 = 40 × 10 = 400 N
Distance from pivot = 2 - 1.5 = 0.5 m
Moment = 400 × 0.5 = 200 Nm
Weight of child 2 = 30 × 10 = 300 N
Let distance from pivot be x, then:
300 × x = 200 → x = 0.67 m
So, the second child must sit 0.67 m from the pivot on the opposite side.
A train decelerates uniformly from 30 m/s to a stop in 20 seconds.
a) What is its acceleration?
a) Use: v = u + at
0 = 30 + a × 20 → a = -30/20 = -1.5 m/s²
A ball of mass 1 kg is dropped from a height of 10 m.
a) What is its potential energy at the start?
b) What is its kinetic energy just before it hits the ground (ignore air resistance)?
a) PE = mgh = 1 × 10 × 10 = 100 J
b) Since energy is conserved (no energy loss), KE just before hitting the ground = 100 J