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Chapter 7: Q27Q (page 170)

If only an external force can change the momentum of the centre of mass of an object, how can the internal force of the engine accelerate a car?

Short Answer

Expert verified

Newton’s third law helps the internal force of the engine to accelerate a car.

Step by step solution

01

Significance of Newton’s third law

According to Newton’s third law, if a body applies force on an object, the object will also exert a reaction force of identical magnitude on the body.

02

Understanding the acceleration of a car

When an engine applies force on the wheel of the automobile, it starts rotating. The rotating wheel pushes the surface of the road backward. A reaction force exerts on the wheel, pushing it forward due to the third law. This way, the car starts to accelerate using the mechanical energy produced by the chemical energy of the fuel.

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Most popular questions from this chapter

At a hydroelectric power plant, water is directed at high speed against turbine blades on an axle that turns an electric generator. For maximum power generation, should the turbine blades be designed so that the water is brought to a dead stop, or so that the water rebounds?

(I) The distance between a carbon atom \(\left( {{\bf{m = 12}}\;{\bf{u}}} \right)\) and an oxygen atom \(\left( {{\bf{m = 16}}\;{\bf{u}}} \right)\) in the CO molecule is \({\bf{1}}{\bf{.13 \times 1}}{{\bf{0}}^{{\bf{10}}}}\;{\bf{m}}\) How far from the carbon atom is the center of mass of the molecule?

A mallet consists of a uniform cylindrical head of mass 2.30 kg and a diameter 0.0800 m mounted on a uniform cylindrical handle of mass 0.500 kg and length 0.240 m, as shown in Fig. 7–42. If this mallet is tossed, spinning, into the air, how far above the bottom of the handle is the point that will follow a parabolic trajectory?

FIGURE 7-42 Problem 62.

A meteor whose mass was about \(1.5 \times {10^8}\;{\rm{kg}}\) struck the Earth \(\left( {{m_{\rm{E}}} = 6.0 \times {{10}^{24}}\;{\rm{kg}}} \right)\) with a speed of about 25 km/s and came to rest in the Earth.

(a) What was the Earth’s recoil speed (relative to Earth at rest before the collision)?

(b) What fraction of the meteor’s kinetic energy was transformed to kinetic energy of the Earth?

(c) By how much did the Earth’s kinetic energy change as a result of this collision?

A novice pool player is faced with the corner pocket shot shown in Fig. 7–49. Relative dimensions are also shown. Should the player worry that this might be a “scratch shot,” in which the cue ball will also fall into a pocket? Give details. Assume equal-mass balls and an elastic collision. Ignore spin.
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