a 75 kg man is standing at rest on ice while holding a 4kg ball. if the man throws the ball at a velocity of 3.50 m/s forward, what will his resulting velocity be?​


Answer 1


His resulting velocity will be 0.187 m/s backwards.



Mass of the man is,

Mass of the ball is,

Initial velocity of the man is,

Initial velocity of the ball is,

Final velocity of the ball is,

Final velocity of the man is,

In order to solve this problem, we apply law of conservation of momentum.

It states that sum of initial momentum is equal to the sum of final momentum.

Momentum is the product of mass and velocity.

Initial momentum = Initial momentum of man and ball

Initial momentum =

Final momentum = Final momentum of man and ball

Final momentum =

Now, initial momentum = final momentum

The negative sign implies backward motion of the man.

Therefore, his resulting velocity is 0.187 m/s backwards.

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If the speed of light in a substance is 2.26 x 10^8 m/s, what is the index of refraction of that substance?





speed of light in vacuum, c = 3 x 10^8 m/s

speed of light in medium, v = 2.26 x 10^8 m/s

The refractive index of the medium is given by

μ = speed of light in vacuum / speed of light in medium

μ = (3 x 10^8) / (2.26 x 10^8)

μ = 1.33


An RV is traveling 60 km/h along a highway. A boy sitting near the driver of the RV throws a ball to another boy at the back end of the RV with a speed of 25 km/h. What is the speed of the ball relative to the boys? km/h What is the speed of the ball relative to a stationary observer on the side of the road? km/h



Speed of the ball relative to the boys: 25 km/h

Speed of the ball relative to a stationary observer: 35 km/h


The RV is travelling at a velocity of

Here we have taken the direction of motion of the RV as positive direction.

The boy sitting near the driver throws the ball back with speed of 25 km/h, so the velocity of the ball in the reference frame of the RV is

with negative sign since it is travelling in the opposite direction relative to the RV. Therefore, this is the velocity measured by every observer in the reference frame of the RV: so the speed measured by the boys is

v = 25 km/h

Instead, a stationary observer outside the RV measures a velocity of the ball given by the algebraic sum of the two velocities:

v = +60 km/h + (-25 km/h) = +35 km/h

So, he/she measures a speed of 35 km/h.


For the question after this one, its 300,000,00 for both


Edge 2021


Coulomb's law for the magnitude of the force FFF between two particles with charges QQQ and Q′Q′Q^\prime separated by a distance ddd is |F|=K|QQ′|d2|F|=K|QQ′|d2, where K=14πϵ0K=14πϵ0, and ϵ0=8.854×10−12C2/(N⋅m2)ϵ0=8.854×10−12C2/(N⋅m2) is the permittivity of free space. Consider two point charges located on the x axis: one charge, q1q1q_1 = -13.5 nCnC , is located at x1x1x_1 = -1.735 mm ; the second charge, q2q2q_2 = 35.5 nCnC , is at the origin (x=0.0000)




The question: What is the net force exerted by these two charges on a third charge q_3 = 47.0 nC placed between q_1 and q_2 at x_3 = -1.240 mm ?

Your answer may be positive or negative, depending on the direction of the force.


The coulomb force is given by the equation

where is the separation between the charges and .

Now, in our case

The separation between charges and is

Therefore, the force between them is

and it is directed in the negative x-direction.

The separation between charges  and is

therefore, the force between them is

Therefore the total force on charge is


A disk-shaped grindstone of mass 1.7 kg and radius 8 cm is spinning at 730 rev/min. After the power is shut off, a woman continues to sharpen her ax by holding it against the grindstone for 9 s until the grindstone stops rotating. (a)What is the angular acceleration of the grindstone?
(b) What is the torque exerted by the ax on the grindstone? (Assume constant angular acceleration and a lack of other frictional torques.)



0.186 N-m        


mass of the grindstone,




final angular velocity,

Initial angular velocity,

Angular acceleration of the grind stone is:

Moment of inertia:

Torque exerted by the ax on the grind stone is:

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