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2 years ago

A grapefruit has a weight on earth of 4.9 newtons. What is the grapefruit's mass?

2 answers:

3 0

Weight = mg where m = mass and g = gravity = 10 (9.81....)
so m = w/g = 4.9 / 10(9.81....) = 0.49 (0.49949....)
if you get given g as 10, answer is 0.49 kg
if you get given g as 9.81, answer is 0.50 (1sf)

igor_vitrenko [27]2 years ago

3 0

Answer:

The grapefruit's mass is 0.5 kg.

Explanation:

Given that,

Weight = 4.9 N

We need to calculate the mass

Using formula of newton's second law

$F = mg$

$m = \dfrac{F}{g}$

Where, F = weight on earth

g = acceleration due to gravity

Put the value into the formula

$m = \dfrac{4.9}{9.8}$

$m =0.5\ kg$

Hence, The grapefruit's mass is 0.5 kg.

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1 A 75-g ball is projected from a height of 1.6 m with a horizontal velocity of 2 m/s and bounces from a 400-g smooth plate supp

Tanzania [10]

Answer with explanation:

We are given that

Mass of ball, $m_1=$ 75 g= $\frac{75}{1000}=0075kg$

1 kg=1000 g

Height, $h_1=1.6 m$

$h_2=0.6 m$

Horizontal velocity, $v_x=2 m/s$

Mass of plate $m_2=400 g=\frac{400}{1000}=0.4 kg$

a.Initial velocity of plate, $u_2=0$

Velocity before impact= $u_1=\sqrt{2gh_1}=\sqrt{2\times 9.8\times 1.6}=5.6m/s$

Where $g=9.8 m/s^2$

Velocity after impact, $v_1=\sqrt{2gh_2}=\sqrt{2\times 9.8\times 0.6}=3.4m/s$

According to law of conservation of momentum

$m_1u_1+m_2u_1=-m_1v_1+m_2v_2$

Substitute the values

$0.075\times 5.6+0=-0.075\times 3.4+0.4v_2$

$0.4v_2=0.075\times 5.6+0.075\times 3.4$

$v_2=\frac{0.075\times 5.6+0.075\times 3.4}{0.4}=1.69 m/s$

Velocity of plate=1.69 m/s

b.Initial energy= $\frac{1}{2}m_1v^2_x+m_1gh_1=\frac{1}{2}(0.075)(2^2)+0.075\times 9.8\times 1.6=1.326 J$

Final energy= $\frac{1}{2}m_1v^2_x+m_1gh_2+\frac{1}{2}m_2v^2_2$

Final energy= $\frac{1}{2}(0.075)(2^2)+0.075\times 9.8\times 0.6+\frac{1}{2}(0.4)(1.69)^2=1.162 J$

Energy lost due to compact=Initial energy-final energy=1.326-1.162=0.164 J

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2 years ago

Consider a loop of wire with a resistor. In the same plane, (with switch S closed) a long wire has a current I flowing from left

Ulleksa [173]

Solution :

The given figure is a loop of a wire with a resistor.

When the switch S is closed for long time and is suddenly opened, the direction of the induced current can be find out by using the rule of right hand screw. According to the right hand screw rule, the direction of the magnetic field at the loop is in the direction that points outwards. The strength of the current rapidly decreases as it is switch off and the magnetic flux that is linked with the loop wire will also decrease.

According to the Lenz's law, the direction of the induced current must be such $\text{that it opposes}$ the decrease in the magnetic flux. It means the direction of the magnetic field must be outwards and also normal to the plane of the screen. The direction of the induced anti clockwise or from right to left in the resistance.

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2 years ago

A high diver dives into a swimming pool. His potential energy at the top is 10,000 J (relative to the surface of the pool). What

Semmy [17]

Answer:

Kinetic energy of diver at 90% of the distance to the water is 9000 J

Explanation:

Let d is the distance between the position of the diver and surface of the pool.

Initially, the diver is at rest and only have potential energy which is equal to 10000 J.

As the diver dives towards the pool, its potential energy is converting into kinetic energy due to law of conservation of energy, as total energy of the system remains same.

Energy before diving = Energy during diving

(Potential Energy + Kinetic Energy) = (Kinetic Energy + Potential Energy)

When the diver reaches 90% of the distance to the water, its kinetic energy

is 90% to its initial potential energy, as its initial kinetic is zero,i.e.,

K.E. = $\frac{90}{100}\times10000$

K.E. = 9000 J

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2 years ago

While on a playground, you and your niece take turns sliding down a frictionless slide. Your mass is 75 kg while your little nie

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Answer:

Explanation:

In absence of friction, total mechanical energy must be conserved.
This means that the change in gravitational potential energy (in magnitude) must be equal to the change in kinetic energy:

$\Delta K = \Delta U \\ \\ \frac{1}{2} * m* v^{2} = m*g*h$

As it can be seen, the mass m is on the both sides of the equation, which means that it can be simplified.
We can solve this equation for v (speed at the bottom) as follows:

$v = \sqrt{2*g*h}$

As it can be seen, the mass has no part in the equation, so, due both are starting from the same height, both people have the same speed at the bottom.
The option c is the right one.

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3 years ago

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katovenus [111]

Answer:

v = (-4.44 i^ + 6.66 j^ ) m/s, a_average =( 0 i^ -2π j^) m/s²

Explanation:

The expression left corresponds to an oscillatory movement (MAS), the speed is defined by

v = dr / dt

the function of position

r = 2 cos πt i^ + 3 sin πt j^

let us note that it is a movement in two dimensions

let's perform the derivative

v = -2π sin πt i^ + 3π cos πt j^

we evaluate this expression for t = 0.25 s, remember that the angle is in radians

v = -2π sin (π 0.25) i^ + 3π cos (π 0.25) j^

v = (-4.44 i^ + 6.66 j^ ) m/s

To calculate the mean acceleration we use the expression

a = ( $v_{f} - v_{o}$ ) / Δt

indicates that the time is the first 3 s

we look for the initial velocity t = 0 s

v₀ = 0 i ^ + 3π j ^

we look for the fine velocity, t = 3 s

v_f = - 2π sin (π 3) + 3π cos (π 3) j ^

v_f = 0 i ^ - 3π j ^

we calculate the average acceleration

Δt = (3 -0) = 3 s

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a_average = (0 i ^ -2π j ^ ) m/s²

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3 years ago