The quarterback throws a football at 25 m/s at a certain angle above the horizontal. If it took the ball 2.5 s to reach the top of its path, how long was it in the air?


Answer 1


The ball was in the air for 5.0 seconds


When the ball is thrown above at a certain angle from the horizontal it follows a projectile motion.

The ball has a specific vertical and horizontal velocity.

The time take for the ball to reach at the top of its path is also the time taken by the vertical velocity vector to become zero. This is the first half of the projectile motion (ball is going up).

For the second half, the ball comes down and it accelerates with same gravitational acceleration from which it was decelerating in the first half. Hence the time to come down will be the same 2.5 seconds.

So the total time the ball was in the air is twice of 2.5, i.e,

5.0 seconds

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How much heat is required to vaporize 1.5kg of liquid water at its boiling point



Water, 1.5kg at boiling point


Heat required to vaporize at boiling point


Water at boiling point is at 100degrees Celsius

Changing it into Kelvin, just dd 273 to 100 = 373 K

H = mCpT

H = (1.5kg)(4.184kJ/kg-K)(373K)

H = 2340.9kJ


Why do you choose MCB in place of a fuse?


It protects the electrical appliance and the person from electrical shocks/faults.

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A cork is held at the bottom of a bucket of water by a piece of string. The actual depth of the cork is 0.6 m below the surface of the water. The density of water is ρ = 1000 kg/m3 and the acceleration of gravity is g = 9.8 m/s2 . 0.6 m If the density of the cork is 150 kg/m3 and the volume of the cork is 2 cm3, then what is the tension in the string?


The tension on the string in the bucket of water is 0.017 N .

The given parameters;

  • depth of the cork, h = 0.6 m
  • density of the water, ρ = 1000 kg/m³
  • density of the cork, = 150 kg/m³
  • volume of the cork, V = 2 cm³

The tension on the string is the buoyant force experienced by the cork is calculated as follows;

Thus, the tension on the string is 0.017 N.

Learn more


tension on the string will be 0.0167 N


ρ = 1000 kg/m³

density of the cork = 150  kg/m³

volume of the cork = 2 cm³

tension on cork (T)  will be acting in down ward direction.

buoyant force (Fₙ) will act in upward direction.

and weight (W) will act in downward direction.

T = Fₙ - W

hence tension on the string will be 0.0167 N


A camera of weight 8.9 newtons is dropped from a drone at a height of 18.6 meters and enters free fall. Assuming no air resistance, what is the final velocity of the camera a moment before it shatters on the ground?



19.09 m/s


u = 0, h = 18.6 m

Use third equation of motion

v^2 = u^2 + 2 g h

v^2 = 0 + 2 x 9.8 x 18.6

v = 19.09 m/s


A beaker of mass 1.3 kg containing 2.8 kg of water rests on a scale. A 3.7 kg block of a metallic alloy of density 4600 kg/m3 is sus- pended from a spring scale and is submerged in the water of density 1000 kg/m3 as shown in the figure.


1) Force read on the upper scale: 33.4 N

2) Force read on the lower scale: 43.0 N



The reading on the upper scale is equal to the net force acting on the block of metallic alloy. The net force is given by:



W is the weight of the block (downward)

B is the buoyant force (upward)

The weight of the block is given by

where m = 3.7 kg is the mass of the block and is the acceleration of gravity.

The buoyant force is given by


is the water density

V is the volume of the block

The volume of the block can be written as

where is the density of the block.

Substituting everything into eq.(1), we find:


Here we want to find the force on the lower scale.

The force on the lower scale is equal to the difference between the total weight of the system (given by the weight of the beaker + the weight of the water + the weight of the block) and the upper net force exerted on the upper scale, therefore:


is the mass of the beaker

is the mass of the water

is the mass of the block

is the upper net force

Substituting and solving, we find:

Learn more about forces and weight:



What is the average speed, over the first 1.0 s of its motion, of a pebble released from rest off a bridge?


By definition, the speed after a time  of the pebble is  where  is the G-force's acceleration.

Therefore the average value over one second is 

Using  we therefore have an average speed of 

24. Which determines the frequency of a sound wave?​



Speed and wave length.


The frequency of a sound wave is also what we would call the pitch, a really fast and short wave lenght will create a high pitch, while a really slow and long wave length would create a low pitch in the sound wave. The formula for frequency is given by the next formula:

As you can see from the formula, it is velocity and wave length that determine the frequency of a soundwave.


Speed and wavelength


Speed and wavelengths are factors that are used to determine the frequency of a sound wave.


Why does turning on the television cause the resistor to heat up?


Because it takes power from the electricity to turn on so it heats up

Two oppositely charged parallel plates are a fixed distance apart. Which phrase best describes the relationship between the electric field intensity (E) between the plates and the potential difference (V) across the plates?



the electric field is proportional to the voltage divided by the separation of the plates,


This parallel plate configuration is widely used, as it creates a uniform electric field between the plates. Where the potential and field differences are related by

              DV = E d

That is, the electric field is proportional to the voltage divided by the separation of the plates, in general all these configurations are called capacitors

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