MHB Mechanics- General motion in a straight line.

[Shah 72]

Iam not able to get the ans for q(a) which is 6.5 m/s
I don't understand how to calculate (b)

 

[DaalChawal]

For (a) part you have to solve a cubic equation $t^3 - 140t + 575 =0 $ and put the value of t in $v=0.3t^2 + 14$ to get final answer.
for (b) part put $v=0 $ to get t for which velocity is zero and put that t in $x= -0.1t^3 +14t$ now you have to solve only.

 

[Shah 72]

For (a) part you have to solve a cubic equation $t^3 - 140t + 575 =0 $ and put the value of t in $v=0.3t^2 + 14$ to get final answer.
for (b) part put $v=0 $ to get t for which velocity is zero and put that t in $x= -0.1t^3 +14t$ now you have to solve only.

I get t= 4.24s
When I substitute this value in v I get -0.3×4.24^2+14. I don't get the ans 6.5 m/s

 

[Shah 72]

For (a) part you have to solve a cubic equation $t^3 - 140t + 575 =0 $ and put the value of t in $v=0.3t^2 + 14$ to get final answer.
for (b) part put $v=0 $ to get t for which velocity is zero and put that t in $x= -0.1t^3 +14t$ now you have to solve only.

Can you also pls guide me how to calculate (c)

 

[DaalChawal]

I get t= 4.24s
When I substitute this value in v I get -0.3×4.24^2+14. I don't get the answer 6.5 m/s

You are making a calculation error, t=4.24 does not satisfy the equation.
For (c) part again you have to solve the cubic equation in t $x =- 0.1t^3 + 14t$ put $x=40$

 

[Shah 72]

For (a) part you have to solve a cubic equation $t^3 - 140t + 575 =0 $ and put the value of t in $v=0.3t^2 + 14$ to get final answer.
for (b) part put $v=0 $ to get t for which velocity is zero and put that t in $x= -0.1t^3 +14t$ now you have to solve only.

Iam so so sorry. I did a mistake. I have to solve the cubic equation. I did the mistake of solving quadratic equation.

 

[Shah 72]

You are making a calculation error, t=4.24 does not satisfy the equation.
For (c) part again you have to solve the cubic equation in t $x =- 0.1t^3 + 14t$ put $x=40$

I realized the mistake. Thank you!

 

[Shah 72]

You are making a calculation error, t=4.24 does not satisfy the equation.
For (c) part again you have to solve the cubic equation in t $x =- 0.1t^3 + 14t$ put $x=40$

Thanks a lottttt! I got all the ans