Question

A child of mass 35 kg rides a bicycle of
mass 15 kg. The force of friction is 20N.
What power must she supply to move at
a speed of 2.0 ms-1 while going up an
incline of slope 30°? Draw the free-body
diagram. Take g = 10 ms-2 4+1
100 rod-1 is​

Answer 1

$\huge\boxed{Answer}$

Force F = 20N .

Mass m = 2.0 kg

Initial velocity u = 0

acceleration, a = 10m/s

2

t = 1 sec.

Now Refer to the attachment, See the free body diagram of the block.

Force works on the block:-

Weight, W = mg

W = 2 × 10

W = 20N (which is Downward)

Normal force N = mg cos37

N = 20 × 0.80

N = 16 N. (perpendicular & upward to the plane )

Here Applied Force, P = 20N (which is down along the plane)

Now For Final Speed, We know the formula:-

v = u + at

v = 0 + 10 × 1

v = 10 m/s

the Distance travelled s = ut + 0.5 at×t

s = 0 + 0.5 ×10×1×1

s = 5 m.

Now,

(a) So work done by the force of gravity in 1 sec. = F × d

= 20 N × 5m

= 100 J.

(b) Here the weight act as downward, so distance travelled in downward.

= 5 × sin37

= 5 × 0.6

= 3 m.

so work done by gravity,

= 20 N × 3 m

= 60 J.

(c) Now, work done by all the forces

= change in Kinetic energy

=

2

1

m(v

2

−u

2

)

= 0.5×2.0×(10

2

−0

2

)

= 100 J.

W.D by frictional force

= work was done by all forces -( work was done by Normal force + work done by applied force + work done by gravity )

= 100 J - (100 + 60 +0 )

= 100 - 160

= -60 J

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