Homework help regarding force, weight , acceleration and momentum

[Bookworm_321]

the question is,( please excuse me if there are any mistakes with grammar or language in particular 
The weight of an object is 5N. At a certain instant, its momentum is  6kgms-1. Due to a force applied in the direction opposite to the direction of motion. The velocity of the object decreased to 4ms-1. What is the force exerted on the object? 

so, the way I tried to solve this was by first finding the mass using the weight  by taking the acceleration as the gravitation force but I took it by rounding 9.8ms^-2 as 10ms^-2 .and I got the mass as 0.5kg.

Then, I used that mass with the formulae of momentum and found the velocity which was 12ms^-1. After that I found the deceleration of the object that was 2ms^-2. And to find the force that was exerted on the object to make it decelerate , I multiplied the mass which I found earlier as 0.5kg and the acceleration as 2ms^-2  and got the answer as 1N. 

is anything wrong in the way I tried to solve this question? If so please correct me where I did wrong 

[studiot]

1 hour ago, Bookworm_321 said:

so, the way I tried to solve this was by first finding the mass using the weight  by taking the acceleration as the gravitation force but I took it by rounding 9.8ms^-2 as 10ms^-2 .and I got the mass as 0.5kg.

Yes

1 hour ago, Bookworm_321 said:

Then, I used that mass with the formulae of momentum and found the velocity which was 12ms^-1.

Yes

1 hour ago, Bookworm_321 said:

After that I found the deceleration of the object that was 2ms^-2

How  ?

 

I think you need to know the time it takes for this to happen or the distance over which it travels during this time.

1 hour ago, Bookworm_321 said:

Due to a force applied in the direction opposite to the direction of motion. The velocity of the object decreased to 4ms-1. What is the force exerted on the object? 

 

Edited May 6, 2021 by studiot

[exchemist]

1 hour ago, Bookworm_321 said:

the question is,( please excuse me if there are any mistakes with grammar or language in particular 
The weight of an object is 5N. At a certain instant, its momentum is  6kgms-1. Due to a force applied in the direction opposite to the direction of motion. The velocity of the object decreased to 4ms-1. What is the force exerted on the object? 

so, the way I tried to solve this was by first finding the mass using the weight  by taking the acceleration as the gravitation force but I took it by rounding 9.8ms^-2 as 10ms^-2 .and I got the mass as 0.5kg.

Then, I used that mass with the formulae of momentum and found the velocity which was 12ms^-1. After that I found the deceleration of the object that was 2ms^-2. And to find the force that was exerted on the object to make it decelerate , I multiplied the mass which I found earlier as 0.5kg and the acceleration as 2ms^-2  and got the answer as 1N. 

is anything wrong in the way I tried to solve this question? If so please correct me where I did wrong 

Agree with @studiot that a piece of information seems to be missing from the problem, in the way you describe it.

You don't say over what period of time the deceleration occurs. Without that, you can't know if the deceleration was gradual, due to a small force applied for a long period of time, or sudden, due to a large force applied over a short period. 

[Bookworm_321]

I am sorry for not mentioning it before  it decelerate in the period of 4 seconds to 4ms^-2 

[studiot]

2 hours ago, Bookworm_321 said:

I am sorry for not mentioning it before  it decelerate in the period of 4 seconds to 4ms^-2 

Ok so

 

22 hours ago, Bookworm_321 said:

After that I found the deceleration of the object that was 2ms^-2

I know you said deceleration, but in your calculations you should use a negative acceleration.

So again how did you arrive at +2m/s² ?

Did you use the formula       v = u + at      ?

[exchemist]

2 hours ago, Bookworm_321 said:

I am sorry for not mentioning it before  it decelerate in the period of 4 seconds to 4ms^-2 

Aha! Now the rest of your calculation makes sense! I see where you get the deceleration of 2m/sec² from (12m/sec -> 4 m/sec over 4 seconds)and given that the mass is 0.5kg, that will imply a force of 1N, just as you say. So it all looks good to me. 

[joigus]

Good members of the community helping along until everything makes sense and OP helping clarify own question. Business as unusual. Thanks to everybody involved.  

[studiot]

Th

1 hour ago, exchemist said:

So it all looks good to me. 

The acceleration needs to be negative so that the calculation gives the correct direction to the calculated forc in the final eauation F = ma.

ie the force is a retarding force.

[exchemist]

1 hour ago, studiot said:

Th

The acceleration needs to be negative so that the calculation gives the correct direction to the calculated forc in the final eauation F = ma.

ie the force is a retarding force.

Strictly, yes of course, but the way this problem has been posed, you don't actually need the sign to get the right answers.

[studiot]

Oh dear was my spelling really that sloppy  ?

😳

Sorry all.