All Mechanics DOUBTS HERE!!!

[spiderman]

hey guys..........................please cud ull help me wit this sum!!


A boy of weight 294N falls 2.5 m onto a trampoline, which brings him to rest after he has descended a further distance of 0.2m. Calculate the k.e of the boy when he reaches the trampoline, and the energy stored in the trampoline when the boy is at rest?

[S.M.A.T]

K.E=WORK DONE=294×2.5=735J
E.P.E=0.5Fx=0.5×294×0.2=29.4J

[spiderman]

But the answer given is  794N for the second part.........

[nid404]

hey guys..........................please cud ull help me wit this sum!!


A boy of weight 294N falls 2.5 m onto a trampoline, which brings him to rest after he has descended a further distance of 0.2m. Calculate the k.e of the boy when he reaches the trampoline, and the energy stored in the trampoline when the boy is at rest?

Total energy stored= 294 X (2.5+0.2)= 793.8 J

[S.M.A.T]

Total energy stored= 294 X (2.5+0.2)= 793.5 J

Can you please explain the answer,the formula for the elastic potential energy is 0.5Fx,where x is the extension.But how come the answer is 793.5J

[nid404]

793.8..modified my post.

Well apparently the potential energy is converted to the elastic potential energy in the trampoline.

[S.M.A.T]

Thanks +rep

[nid404]

Not a problem 

[nid404]

I have a doubt 

A racing car of mass 2000kg accelerates with a driving force of 480(t-10)² newtons until it reaches its maximum speed after 10seconds. Find its maximum speed,and the distance it travels in reaching this speed.

I don't know even know how to begin -_-

[nid404]

And yes I do feel extremely dumb...

[cooldude]

I have a doubt 

A racing car of mass 2000kg accelerates with a driving force of 480(t-10)² newtons until it reaches its maximum speed after 10seconds. Find its maximum speed,and the distance it travels in reaching this speed.

I don't know even know how to begin -_-

F=ma
a=480(t-10)^2/2000
we integrate with the limits 10 and 0 to find the max vel, and then integrate the velocity again with limits 10 and 0 to find the distance travelled.

[S.M.A.T]

Here

[nid404]

Thank you guys +rep

[haris94]

some1 pls help me with this
the question is killing me

as the car passes a point A, its speed is 10m/s. the car moves with constant acceleration 'a'm/s² along the road for 'T' seconds until it reaches a point B where the speed is 'V'm/s. the car travels at this speed for a further 10 seconds to reach a point C. from C, it travels for a further 'T' seconds with constant acceleration 3'a'm/s² until it reaches a speed of 20m/s at point D. sketch a tv graph of motion and show that 'V' is 12.5m/s. given that the distance between A and D is 675m, find the value of 'a' and 'T'.

pls answer asap
Thanks

[astarmathsandphysics]

here