Force and Impulse physics problem

• Mandy89
In summary: maybe if he has a better understanding of these concepts he can start to do the integration himself. andsecond of all, maybe if he could provide me with an equation for mv_b that would be great.

Mandy89

I attempted the qn .. but I'm not sure if this is the correct way of going about it..
the relevant equations used weren't given.

Homework Statement

Force and Impulse:

The magnitude of an unbalanced force on a 10 kg object increases at a constant rate from 0N to 50N in 4.0s, causing the initially stationary object to move.

What is the speed of the object at the end of the 4.0s?

[not sure] ..
mv = Ft ??

The Attempt at a Solution

v = Ft / m = (50N)(4.0s) / (10kg) = 20m/s

Thanks for any help = ) very appreciated

- mandy : )

This would involve integration...since the force is UNBALANCED.
Do you have any concept regarding it?

does it have something to do with

F = ma = m(dv/dt) ??

= S .. i honestly have no idea what to do with it

yupp and intergral from the given displacement.
if you want the concept reply for it.

yes could i please have the concept ..
thanks for your help : )

The simple way to do this problem is to recognize that if the force increases by a constant rate, you can simply use the average of the initial and final forces as the average force applied for the entire time. In your example, the average force would be 25 N applied for 4 seconds, giving you an impulse of 100 kg m/s

You can see why you can use 25 N as the average force if you actually do out the integration. What you have is

$$F = ma = m\frac{dv}{dt} \implies F dt = m dv \implies \int_{t_a}^{t_b} F dt = \int_{v_a}^{v_b} m dv = mv_b$$

because $v_a = 0$.

Now, what is the force F? Remember that it increases at a constant rate from 0 to 50 N in 4 seconds. Since it increases at a constant rate, F must be linear.

Last edited:
Tedjn said:
The simple way to do this problem is to recognize that if the force increases by a constant rate, you can simply use the average of the initial and final forces as the average force applied for the entire time. In your example, the average force would be 25 N applied for 4 seconds, giving you an impulse of 100 kg m/s

You can see why you can use 25 N as the average force if you actually do out the integration. What you have is

$$F = ma = m\frac{dv}{dt} \implies F dt = m dv \implies \int_{t_a}^{t_b} F dt = \int_{v_a}^{v_b} m dv = mv_b$$

because $v_a = 0$.

Now, what is the force F? Remember that it increases at a constant rate from 0 to 50 N in 4 seconds. Since it increases at a constant rate, F must be linear.

first of all let him have a concept of integration and differentiation.

1. What is the difference between force and impulse?

Force is a physical quantity that describes the push or pull on an object, while impulse is the change in momentum of an object. Force is measured in Newtons (N), while impulse is measured in Newton-seconds (Ns).

2. How are force and impulse related?

Force and impulse are related through the equation FΔt = mΔv, where F is the force applied, Δt is the time interval in which the force is applied, m is the mass of the object, and Δv is the change in velocity of the object. This equation shows that a larger force or longer time interval will result in a greater change in momentum, or impulse.

3. What is the principle of conservation of momentum?

The principle of conservation of momentum states that the total momentum of a system remains constant if there are no external forces acting on the system. This means that the total momentum before an event is equal to the total momentum after the event.

4. How does impulse affect the motion of an object?

Impulse causes a change in an object's momentum, which in turn affects its motion. A larger impulse will result in a greater change in momentum and therefore a greater change in velocity. This can cause an object to speed up, slow down, or change direction.

5. How can I calculate the impulse of an object?

The impulse of an object can be calculated using the equation FΔt = mΔv, where F is the force applied, Δt is the time interval in which the force is applied, m is the mass of the object, and Δv is the change in velocity of the object. Alternatively, the impulse can also be calculated by multiplying the average force applied by the time interval in which it is applied.