In a TV picture tube, electrons are ejected from the cathode with negligible speed and reach a velocity of 5 × 10 6 m s - 1 in travelling one centimetre . Assuming straight line motion, find the constant force exerted on the electron. The mass of the electron is 9 · 1 × 10 - 31 kg .

Given, initial velocity of the electrons is negligible, u = 0 Final velocity of the electrons, v = 5 × 10 6 m s - 1 Distance travelled by the electrons, s = 1 cm = 1 × 10 - 2 m Using the third equation of motion, v 2 = u 2 + 2 a s ⇒ 5 × 10 6 2 = 0 2 + 2 × a × 10 - 2 ⇒ a = 25 × 10 12 2 × 10 - 2 = 1 . 25 × 10 15 m s - 2 Using Newton's second law of motion, F = m a ⇒ F = 9 . 1 × 10 - 31 × 1 . 25 × 10 15 = 11 . 375 × 10 - 16 ≈ 1 . 1 × 10 - 15 N .

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Important Questions on Newton's Laws of Motion

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>OBJECTIVE II>Q 8

A particle is observed from two frames

S_{1}

and

S_{2}

. The frame

S_{2}

moves with respect to

S_{1}

with an acceleration

a

. Let

F_{1}

and

F_{2}

be the pseudo forces on the particle when seen from

S_{1}

and

S_{2}

respectively. Which of the following are not possible?

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>OBJECTIVE II>Q 9

A person says that he measured the acceleration of a particle to be non-zero while no force was acting on the particle.

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>EXERCISES>Q 1

A block of mass

2 kg

placed on a long frictionless horizontal table is pulled horizontally by a constant force

F

. It is found to move

10 m

in the first two seconds. Find the magnitude of

F

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>EXERCISES>Q 2

A car moving at

40 km h^{- 1}

is to be stopped by applying brakes in the next

4.0 m

. If the car weighs

2000 kg

what average force must be applied on it?

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>EXERCISES>Q 3

In a TV picture tube, electrons are ejected from the cathode with negligible speed and reach a velocity of

5 \times 10^{6} m s^{- 1}

in travelling one

centimetre

. Assuming straight line motion, find the constant force exerted on the electron. The mass of the electron is

9 \cdot 1 \times 10^{- 31} kg

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>EXERCISES>Q 4

A block of mass

0.2 kg

is suspended from the ceiling by a light string. The second block of mass

0.3 kg

is suspended from the first block through another string. Find the tensions in the two strings. Take

g = 10 m s^{- 2}

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>EXERCISES>Q 5

Two blocks of equal mass

m

are tied to each other through a light string and placed on a smooth horizontal table. One of the blocks is pulled along the line joining them with a constant force

F

. Find the tension in the string joining the blocks.

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CONCEPTS OF PHYSICS [VOLUME 1]>Chapter 5 - Newton's Laws of Motion>EXERCISES>Q 6

A particle of mass $50 g$ moves on a straight line. The variation of speed with time is shown in the figure. Find the force acting on the particle at $t = 2$ , $4$ and $6 seconds$ .

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Important Questions on Newton's Laws of Motion

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