Question

A car is running at a speed of 15 km/h while another car is moving at a speed of 500 m/min.Find the ratio of their kinetic energies.



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Answer 1

Answer:

orce acting on the body = 10 kgf = 10 x 10 N = 100 N

Displacement, S=0.5 m

Work done= force x displacement in the direction of force

(i)W =F x S

W = 100 x 0.5= 50 J

(ii)Work = force x displacement in the direction of force

W = F x S cosConcise-physics-part-ii-selina Solutions Icse Class 10 Physics Chapter - Work Energy And Power

W = 100 x 0.5 cos60o

W= 100 x0.5 x 0.5(cos60o=0.5)

W=25 J

(iii)Normal to the force:

Work = force x displacement in the direction of force

W = F x S cosConcise-physics-part-ii-selina Solutions Icse Class 10 Physics Chapter - Work Energy And Power

W = 100 x 0.5 cos90o

W= 100 x 0.5 x 0 =0 J(cos90o =0)Explanation:

Answer 2

Answer:

1:4

Explanation:

It is like one car is moving with v speed and other with 2v speed because one is 15 km/h and other is 30 km/h .

K.E=0.5×m×v

2

K.E(1st)=0.5×m×v

2

K.E(2nd)=0.5×m×(2v)

2

Hence the ratio is 0.5×m×v

2

:0.5×m×(2v)

2

=1:4

Hence the ratio is 1:4.