Answered

A car traveling with constant speed travels 150 km in 7200 s. What is the speed of the car?



Answer :

75 km/hr, so  in other words 75 km per hour.

7200 s / 60 = 120 min
120 min / 60 =2 hr
so 150 km / 2 hr = 75 km per hour

Answer:

The speed of the car is [tex]\boxed{75\,{{{\text{km}}} \mathord{\left/{\vphantom {{{\text{km}}} {{\text{hr}}}}} \right.\kern-\nulldelimiterspace} {{\text{hr}}}}}[/tex] or [tex]\boxed{20.83\,{{\text{m}} \mathord{\left/{\vphantom {{\text{m}} {\text{s}}}} \right.\kern-\nulldelimiterspace} {\text{s}}}}[/tex] .

Further Explanation:

Given:

The distance covered by the car is [tex]150\,{\text{km}}[/tex].

The time taken by the car to cover the distance is [tex]7200\,{\text{s}}[/tex] .

Concept:

The speed of a car is the ratio of the distance covered by the car to the time taken by the car in covering the distance.

The expression for the speed of the car is:

[tex]v = \dfrac{d}{t}[/tex]       …… (1)                                      

Here, [tex]v[/tex] is the speed of the car, [tex]d[/tex] is the distance covered and [tex]t[/tex] is the time taken by the car.

Substitute the value of distance and time in the above expression.

 [tex]\begin{aligned}v &= \frac{{150\,{\text{km}}}}{{7200\,{\text{s}}\left( {\frac{{1\,{\text{hr}}}}{{60 \times 60\,{\text{s}}}}} \right)}}\\&= \frac{{150}}{2}\,{{{\text{km}}} \mathord{\left/{\vphantom {{{\text{km}}} {{\text{hr}}}}} \right.\kern-\nulldelimiterspace} {{\text{hr}}}}\\&= 75\,{{{\text{km}}} \mathord{\left/{\vphantom {{{\text{km}}} {{\text{hr}}}}} \right.\kern-\nulldelimiterspace} {{\text{hr}}}}\\\end{aligned}[/tex]

The speed of the car in terms of [tex]{{\text{m}} \mathord{\left/{\vphantom {{\text{m}} {\text{s}}}} \right.\kern-\nulldelimiterspace} {\text{s}}}[/tex]  can be expressed as.

[tex]\begin{aligned}v&=75\,{{{\text{km}}} \mathord{\left/{\vphantom {{{\text{km}}}{{\text{hr}}}}} \right.\kern-\nulldelimiterspace} {{\text{hr}}}}\left( {\frac{{1000\,{\text{m}}}}{{3600\,{\text{s}}}}} \right)\\&=75 \times\frac{5}{{18}}\,{{\text{m}} \mathord{\left/{\vphantom {{\text{m}} {\text{s}}}} \right.\kern-\nulldelimiterspace} {\text{s}}}\\&= 20.83\,{{\text{m}} \mathord{\left/{\vphantom {{\text{m}} {\text{s}}}} \right.\kern-\nulldelimiterspace} {\text{s}}}\\\end{aligned}[/tex]

Thus, the speed of the car is [tex]\boxed{75\,{{{\text{km}}} \mathord{\left/{\vphantom {{{\text{km}}} {{\text{hr}}}}} \right.\kern-\nulldelimiterspace} {{\text{hr}}}}}[/tex] or [tex]\boxed{20.83\,{{\text{m}} \mathord{\left/{\vphantom {{\text{m}} {\text{s}}}}\right.\kern-\nulldelimiterspace} {\text{s}}}}[/tex].

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Answer Details:

Grade:Middle School

Chapter:Speed and distance

Subject:Physics

Keywords: Speed, velocity, distance, time, distance of 150 km, in 7200 s, speed of the car, ratio of distance, rate of change of distance.

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