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AfilCa [17]
2 years ago
5

A student has an 80 g sample of a radioactive material that has a half-life of 20 seconds. How much material will he have left a

fter 60 seconds?
A.
10 g

B.
20 g

C.
40 g

D.
5 g
Physics
1 answer:
Juliette [100K]2 years ago
7 0
The answer is C 40 g
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Formula for the distance (d) is given by d = rate*time. For example if you are traveling at 60 mph for 3 hours the distance trav
babunello [35]

Explanation:

Distance covered by the particle is given by:

Distance (d) = rate (v) × time (t)                

Speed of Mary, v₁ = 50 mph

Speed of Jim, v₂ = 60 mph

It is assumed that, Mary and Jim leave at the same time. After one hour, Jim is 10 miles ahead.

Distance travelled by Jim, d₁ = (60t + 10)

Distance travelled by Mary, d₂ = 50t

The distance between Mary and Jim is greater than or equal to 100 miles.

60t+10-50t\ge100

10t\ge90

t\ge9\ h

So, Jim takes is 9 hours more than Mary to cover same distance. Hence, this is the required solution.

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3 years ago
Need help identifying the rest of the elements!
gregori [183]
I think that number five is lithium
6 0
2 years ago
A child on a swing sweeps out a distance of 45 ft on the first pass. If she is allowed to continue swinging until she​ stops, an
earnstyle [38]

Answer:

d = 90 ft

Explanation:

Here in each swing the distance sweeps by the swing is half of the initial distance that it will move

So here we can say that total distance in whole motion is  given as

d = 45 + \frac{45}{2} + \frac{45}{4} + \frac{45}{8}..........

since it is half of the distance that it will move in each swing so it would be a geometric progression with common ratio of 1/2

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S = \frac{a}{1 - r}

d = \frac{45}{1 - \frac{1}{2}}

d = 90 ft

6 0
3 years ago
A ball rolls down the hill which has a vertical height of 15 m. Ignoring friction what would be the gravitational potential ener
trasher [3.6K]

a) Potential energy: 147 m [J]

The gravitational potential energy of an object is given by

U=mgh

where

m is its mass

g=9.8 m/s^2 is the acceleration of gravity

h is the height of the object above the ground

In this problem,

h = 15 m

We call 'm' the mass of the ball, since we don't know it

So, the potential energy of the ball at the top of the hill is

U=(m)(9.8)(15)=147 m (J)

b) Velocity of the ball at the bottom of the hill: 17.1 m/s

According to the law of conservation of energy, in absence of friction all the potential energy of the ball is converted into kinetic energy as the ball reaches the bottom of the hill. Therefore we can write:

U=K=\frac{1}{2}mv^2

where

v is the final velocity of the ball

We know from part a) that

U = 147 m

Substituting into the equation above,

147 m = \frac{1}{2}mv^2

And re-arranging for v, we find the velocity:

v=\sqrt{2\cdot 147}=17.1 m/s

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3 years ago
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allsm [11]
Fnet = (mass) (acceleration)
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