Answer:
5kgm
Explanation:
convert cm to m and g to kg
250/1000=0.25kg
5/1000=0.05m
then find the density
density=mass/volume
=0.25kg/0.05m
=5kgm
Answer:
37.34372 kg
Explanation:
m = Mass
= Change in temperature
1 denotes water
2 denotes copper
c = Heat capacity
Heat is given by

In this case the heat transfer will be equal

Mass of copper block is 37.34372 kg
The average power is 
Explanation:
First of all, we calculate the work done to accelerate the car; according to the work-energy theorem, the work done is equal to the change in kinetic energy of the car:
where
:
is the final kinetic energy of the car, with
m = 2000 kg is the mass of the car
v = 60 m/s is the final speed of the car
is the initial kinetic energy of the car, with
u = 30 m/s is initial speed of the car
Soolving:
Now we can find the power required for the acceleration, which is given by

where
t = 9 s is the time elapsed
Solving:

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If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy. It is a true statement .
Kinetic energy is the energy that an object possesses due to its motion. It is basically the energy of mass in motion. Kinetic energy can never be negative and it is a scalar quantity i.e. it provides only the magnitude and not the direction.
According to law of conservation of mechanical energy change in potential energy is equal and opposite to the change in the kinetic energy.
According to the principle of conservation of mechanical energy, The total mechanical energy of a system is conserved i.e., the energy can neither be created nor be destroyed; it can only be internally converted from one form to another if the forces doing work on the system are conservative in nature.
since, potential energy is stored in the form of work done
Work done = Fs cos (theta)
If force always acts perpendicular to an object's direction of motion
theta = 90 °
cos (90 ) = 0
Work done = 0
since , there is no work done , hence kinetic energy will not change
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