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weqwewe [10]
3 years ago
6

A car skids 18 m on a level road while trying to stop before hitting a stopped car in front of it. The two cars barely touch. Th

e coefficient of kinetic friction between the first car and the road is 0.80. A policewoman gives the driver a ticket for exceeding the 35 mi/h speed limit.
Determine the initial speed of the car.
Physics
1 answer:
nata0808 [166]3 years ago
5 0

Answer:

16.80856 m/s or 37.6 mph

Explanation:

t = Time taken

u = Initial velocity

v = Final velocity = 0

s = Displacement = 18 m

a = Acceleration

g = Acceleration due to gravity = 9.81 m/s²

a=-\frac{f}{m}\\\Rightarrow a=-\frac{\mu mg}{m}\\\Rightarrow a=-\mu g

v^2-u^2=2as\\\Rightarrow v^2-u^2=2(-\mu g)s\\\Rightarrow -u^2=2(-\mu g)s-v^2\\\Rightarrow u=\sqrt{v^2-2(-\mu g)s}\\\Rightarrow u=\sqrt{0^2-2\times (-9.81\times 0.8)\times 18}\\\Rightarrow u=16.80856\ m/s

The initial speed of the car is 16.80856 m/s

Converting to mph

1\ m/s=\frac{1}{1609.34}\times 3600\ mph

16.80856\ m/s=16.80856\times \frac{1}{1609.34}\times 3600\ mph=37.6\ mph

The initial speed of the car is 37.6 mph

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A stationary speed gun emits a microwave beam at 2.10*10^10Hz. It reflects off a car and returns 1030 Hz higher. What is the spe
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Answer: V = 15 m/s

Explanation:

As  stationary speed gun emits a microwave beam at 2.10*10^10Hz. It reflects off a car and returns 1030 Hz higher. The observed frequency the car will be experiencing will be addition of the two frequency. That is,

F = 2.1 × 10^10 + 1030 = 2.100000103×10^10Hz

Using doppler effect formula

F = C/ ( C - V) × f

Where

F = observed frequency

f = source frequency

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V = speed of the car

Substitute all the parameters into the formula

2.100000103×10^10 = 3×10^8/(3×10^8 -V) × 2.1×10^10

2.100000103×10^10/2.1×10^10 = 3×108/(3×10^8 - V)

1.000000049 = 3×10^8/(3×10^8 - V)

Cross multiply

300000014.7 - 1.000000049V = 3×10^8

Collect the like terms

1.000000049V = 14.71429

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V = 14.7 m/s

The speed of the car is 15 m/s approximately.

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