Physics Year 11 easy question!! (1 Viewer)

[ST2010]

1) A rocket travelling at 5.50 x 10^1 fired giving a thrust of 1.880 x 10^3N. At the end of 6.2secs its velocity was 6.378 x 10^2. What was the average mass of the rocket?





2) The force applied by the fan to a glider of mass 850g was 0.34N. How long did it take for the glider to travel 80cm if it started from rest?




workings out thanks ^^

 

[AndrewCase1337]

1st one.

A rocket travelling at 5.50 x 10^1 fired giving a thrust of 1.880 x 10^3N. At the end of 6.2secs its velocity was 6.378 x 10^2

F = MA

F = M ( (Final Velocity - Initial velocity) / Time )

1.88 x 10^3 = M x ((6.378 x 10^2)-(5.5x10)) / 6.2

M = 1.88 x 10^ 3 / ( ( (6.378 x 10^2)-(5.5x10)) / 6.2)

M = 20kg

I guess average mass is trying to throw you off, the question requires more if they tell you a rate at which fuel burns and how much it has.

 

[cutemouse]

1) A rocket travelling at 5.50 x 10^1 fired giving a thrust of 1.880 x 10^3N. At the end of 6.2secs its velocity was 6.378 x 10^2. What was the average mass of the rocket?

F=ma
T-mg=ma
T=m(g+a)
5.50 x 10^1=m(9.8+(6.378 x 10^2))
m=(5.50 x 10^1)/(9.8+(6.378 x 10^2)), and use a calculator, should be correct unless I've made some stupid error.

2) The force applied by the fan to a glider of mass 850g was 0.34N. How long did it take for the glider to travel 80cm if it started from rest?

F=ma
0.34=0.85a
a=0.34/0.85

S=ut+(at^2)
0.8=0+(0.34/0.85)t^2 <-- solve for positive value of t etc...

 

[cutemouse]

Ahh crap... Yes that's the correct formula above.

Thanks for pointing that out.