Solve Momentum Question: 5kg Object, 15 kg m/s, 8 m/s in 15s

[zaga04]

Homework Statement

1. A 5kg object has a momentum of 15 kg m/s. What is the net force required to accelerate the object to 8 m/s over 15 seconds?
A) .35N
B) 1.7N
C) 5.1 N
D) 11 N
E) 23 N

Homework Equations

F=deltaP/deltaT

The Attempt at a Solution

So I use that formula (which I am not sure is right). so wouldn't it be mv/t. So, (5)(8)/15 which is 2.67N which is not an answer choice.

I think I am using the wrong formula, but it's all I can think of! Please help.

 

[kuruman]

The acceleration is not v/t in this case. The object has initial velocity because its momentum is 15 kg m/s before it starts accelerating.

 

[kerimek]

Your attempt at a solution is a good start, but you are using the wrong formula. The formula you are using, F=deltaP/deltaT, is for calculating the average force over a period of time. In this case, we are given the final velocity and time, but not the initial velocity, so we cannot use this formula.

Instead, we can use the formula F=m*a, where F is the net force, m is the mass of the object, and a is the acceleration. We can rearrange this formula to solve for the acceleration, a=F/m. Then, we can use the formula for acceleration, a=(vf-vi)/t, where vf is the final velocity, vi is the initial velocity, and t is the time.

So, we have a=F/m=(vf-vi)/t. Rearranging this equation to solve for the net force, we get F=m*(vf-vi)/t. Plugging in the given values, we get F=(5kg)*(8m/s-0m/s)/15s=5.33N. This is closest to answer choice B) 1.7N, which is the correct answer. So the net force required to accelerate the object from rest to 8 m/s in 15 seconds is 1.7N.