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Worked examples
Twenty questions from this topic with their answer and the method used. Start the quiz above to practise with other variants.
A device transfers 1860 J in 10 s. Average power in watts?
Answer 186
P = E/t = 1860/10 = 186 W.
An ohmic resistor carries 2 A at 20 V. Resistance in ohms?
Answer 10
R = U/I = 20/2 = 10 Ω.
A 340 g sample occupies 10 cm³. Density in g/cm³?
Answer 34
ρ = m/V = 340/10 = 34 g/cm³.
A constant current of 42 A flows for 5 s. Charge transferred in coulombs?
Answer 210
Q = It = 42 × 5 = 210 C.
A constant 70 N force acts over 4 m in the direction of motion. Work in joules?
Answer 280
W = Fd = 70 × 4 = 280 J.
An object travels 195 m in 3 s at constant speed. Speed in m/s?
Answer 65
v = d/t = 195/3 = 65 m/s.
A mass of 16 kg moves at 4 m/s. Kinetic energy in joules (classical mechanics)?
Answer 128
E = ½mv² = ½ × 16 × 4² = 128 J.
A mass of 38 kg accelerates at 3 m/s². Net force in newtons?
Answer 114
F = ma = 38 × 3 = 114 N.
A device transfers 1140 J in 10 s. Average power in watts?
Answer 114
P = E/t = 1140/10 = 114 W.
An ohmic resistor carries 2 A at 84 V. Resistance in ohms?
Answer 42
R = U/I = 84/2 = 42 Ω.
A 780 g sample occupies 10 cm³. Density in g/cm³?
Answer 78
ρ = m/V = 780/10 = 78 g/cm³.
A constant current of 22 A flows for 5 s. Charge transferred in coulombs?
Answer 110
Q = It = 22 × 5 = 110 C.
A constant 95 N force acts over 4 m in the direction of motion. Work in joules?
Answer 380
W = Fd = 95 × 4 = 380 J.
An object travels 300 m in 3 s at constant speed. Speed in m/s?
Answer 100
v = d/t = 300/3 = 100 m/s.
A mass of 11 kg moves at 4 m/s. Kinetic energy in joules (classical mechanics)?
Answer 88
E = ½mv² = ½ × 11 × 4² = 88 J.
A mass of 50 kg accelerates at 3 m/s². Net force in newtons?
Answer 150
F = ma = 50 × 3 = 150 N.
A device transfers 180 J in 10 s. Average power in watts?
Answer 18
P = E/t = 180/10 = 18 W.
An ohmic resistor carries 2 A at 152 V. Resistance in ohms?
Answer 76
R = U/I = 152/2 = 76 Ω.
A 480 g sample occupies 10 cm³. Density in g/cm³?
Answer 48
ρ = m/V = 480/10 = 48 g/cm³.
A constant current of 5 A flows for 5 s. Charge transferred in coulombs?
Answer 25
Q = It = 5 × 5 = 25 C.