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Lana71 [14]
3 years ago
12

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

ed of the car? PLS HELP
Physics
1 answer:
lana [24]3 years ago
3 0

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

C = speed of light = 3×10^8

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

Make V the subject of formula

V = 14.71429/1.000000049

V = 14.7 m/s

The speed of the car is 15 m/s approximately

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Assignments
sladkih [1.3K]

Hello there!

I hope you and your family are staying safe and healthy during this unprecendented time.

A) What is the work done?

Answer: We need to use the formula

w=-F_f(d)

w=-(35)(20)

w=-700J

B) What is the work done on the cart by the gravitational force?  

Alright, we know that the gravitional force is perpendicular to the diplacement. Therefore, we gonna use the following formula:

w=Fdcos90

w=0

C) What is the work done on the cart by the shopper?

This is the easier part, since we already know that the work done by the shopper is the same as the work done by the friction force

W shopper + W friction = 0\\W shopper = W-friction \\W shopper = 700J

D) Find the force the shopper exerts, using energy considerations.

F_f+Fcos25=0\\-35+Fcos25=0\\F=38.6N

E) What is the total work done?

You just need to add them:

w=wshopper+wfriction\\w=0

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