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polet [3.4K]
3 years ago
13

Some kids are playing by rolling a skateboard across level ground beside a 0.75 m high wall. The goal is to drop from the wall v

ertically downward onto the skateboard as it passes by. A 45 kg kid manages to land on the 4.5 kg skateboard as it is passing by at 8 m/s, and they move off together horizontally. If the kid is able to stay on, what will be the speed of the kid and skateboard together
Physics
1 answer:
lys-0071 [83]3 years ago
7 0

Answer:

The speed of the kid and the skateboard together is 0.723 m/s

Explanation:

Let the mass of the kid be m_{k} = 45 kg

Let the mass of the skateboard be m_{s} = 4,5 kg

The initial speed of the skateboard, v_{s} = 8 m/s

The initial horizontal speed of the boy as he jumps on the skateboard, v_{k} = 0 m/s

Let the speed of the kid and the skateboard together be v

According to the principle of conservation of momentum:

m_{k} v_{k} + m_{s} v_{s} = (m_{k} + m_{s}) v

Substituting the appropriate values into  the given equation

(45*0) + (4.5*8) = (45 + 4.8) v

36 = 49.8 v

v = 36/49.8

v = 0.723 m/s

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Amber asked her roommate to turn down the radio because she was trying to study. Her roommate had increased the volume from a vo
Blizzard [7]

Answer:

Difference threshold or also Just Noticeable Difference

Explanation:

The above mentioned case between room mates, where one room mate was able to detect a minute change in volume shows an instance of the difference threshold.

Difference threshold can be defined as stimulation at its minimum level that can be detected by an individual almost 50 % of the times.

It is the lowest possible level of sound that is detectable by a person.

That is what happened in the mentioned case that when the volume was increased from 14 to 15, Amber was able to detect it.

7 0
3 years ago
Which of these is most likely to produce radioactive waves?
Ivan
<h2>Answer:</h2>

<u>A. A nuclear power plant</u> produces radioactive wave.

<h2>Explanation:</h2>

A plant in which a nuclear reactor is used as a source to produce heat is known as nuclear power plant. The heat formed by the reactor is used to form steam which can be used to drive turbines to produce electricity.

The coolant in reactor gets heated by the fission process taking place in the reactor. It is a cyclic process where the steam is condensed and reverted back. A nuclear power plant in active condition produce a small amount of radiation which can be sensed within a radius of 50 miles.  

6 0
3 years ago
Can you please help quick
Mademuasel [1]

Answer:

1. the difference between a series circuit and parallel are if a bulb goes out in a series circuit all go out and in a parallel if one goes out all the others stay on.

2. the function of a switch is to determine if the circuit is closed or open and how is stays on.

Explanation:

5 0
3 years ago
Read 2 more answers
17. A distance-time graph indicates that an object moves 120 meters in 5 seconds and then remains at rest for 5 seconds. What is
irina1246 [14]

Answer:

12 m/s

Explanation:

Speed is distance moved per unit time and expressed as

S=d/t

S is speed, d is distance and t is time.

When at rest for five minutes, distance moved is zero hence speed is 0/5=0 m/s

When having moved 120 m for 5 s then speed is

S=120/5=24 m/s

Average speed is the average of these two speeda

Average speed=(24+0)÷2=24/2=12 m/s

Therefore, average speed is 12 m/s

3 0
3 years ago
Radiation makes it impossible to stand close to a hot lava flow. Calculate the rate of heat transfer by radiation, in kW, from 1
Leya [2.2K]

Answer:

1.5 x 10⁵ W

Explanation:

A = Area of the fresh lava = 1.02 m²

T = Temperature of fresh lava = 1000 °C = 1000 + 273 = 1273 K

T₀ = Temperature of surrounding = 25.3 °C = 25.3 + 273 = 298.3 K

ε = emissivity of the lava = 0.97

σ = stefan's constant = 5.67 x 10⁻⁸ Wm⁻²K⁻⁴

Rate of  transfer is given as

E = σ ε A (T⁴ - T₀⁴)

E = (5.67 x 10⁻⁸) (0.97) (1.02) ((1273)⁴ - (298.3)⁴)

E = 1.5 x 10⁵ W

3 0
3 years ago
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