# Calculating Car Mass with Constant Speed on a Bridge

• Lee80
In summary: The bridge takes 30s to cross entirely. The car creates a force of 3000N.In summary, a car traveling at a constant speed of 20m/s crosses a bridge in 30 seconds and creates a force of 3000N. The question of calculating the mass of the car when it is on the bridge is unclear due to missing information.
Lee80
If a car is traveling towards a bridge at a constant speed of 20ms-1. The bridge takes 30s to cross entirely. The car creates a force of 3000N. Calculate the mass of the car when it is on the bridge.

a=(v2-v1)/t
F=ma

I figured that a = 0 due to the fact that the car is traveling at constant speed.
If a = 0 then isn't it impossible for the car to create a force of 3000N? I am very confused?

Lee80 said:
If a car is traveling towards a bridge at a constant speed of 20ms-1. The bridge takes 30s to cross entirely. The car creates a force of 3000N. Calculate the mass of the car when it is on the bridge.a=(v2-v1)/t
F=ma

I figured that a = 0 due to the fact that the car is traveling at constant speed.
If a = 0 then isn't it impossible for the car to create a force of 3000N? I am very confused?
First,the speed is expressed as m/s not ms-1.
When does the car create a force of 3000N?On the start of bridge?

Edit:Oh I forgot.Welcome to PF

Last edited:
Lee80 said:
If a car is traveling towards a bridge at a constant speed of 20ms-1. The bridge takes 30s to cross entirely. The car creates a force of 3000N. Calculate the mass of the car when it is on the bridge.

a=(v2-v1)/t
F=ma

I figured that a = 0 due to the fact that the car is traveling at constant speed.
If a = 0 then isn't it impossible for the car to create a force of 3000N? I am very confused?

Hi Lee80! http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

I'm a little confused by the question, too. Perhaps the bridge is curved, maybe semicircular? It is not clear whether this 3000N is a vector sum of multiple forces, including also that force known as the vehicle's weight.

Are you sure you have quoted the question details in full?

Last edited by a moderator:
Thanks for the welcome! :)
I have written the question exactly the way it is on the page including the ms-1, which i know is supposed to be superscript but isn't it interchangable with m/s? Anyway the only extra info given was a second part to the question which asks "The bridge can support a mass of 5 tonne or less safely. Is it safe for the car to travel across the bridge?"
I don't think the question is correct? I think it needs more info. The question is supposed to be aimed at year 11 physics.

Lee80 said:
I have written the question exactly the way it is on the page
Pity, because it sounded like the basis of a good question: "If the bridge is of level height but curves around the coastline in a semicircular arc, determine that radius of curvature, and the length of the bridge ..."

including the ms-1, which i know is supposed to be superscript but isn't it interchangable with m/s?
Sure is.

Anyway the only extra info given was a second part to the question which asks "The bridge can support a mass of 5 tonne or less safely. Is it safe for the car to travel across the bridge?"
I don't think the question is correct? I think it needs more info. The question is supposed to be aimed at year 11 physics.
There is either too much information provided, or else not enough. But something's amiss.

Lee80 said:
Thanks for the welcome! :)
I have written the question exactly the way it is on the page including the ms-1, which i know is supposed to be superscript but isn't it interchangeable with m/s?

Yes, if the -1 is a superscript then they're interchangeable.

Use the X2 icon above the message box for superscripts.

m/s is ms-1 .

## 1. How do you calculate the mass of a car on a bridge?

The mass of a car on a bridge can be calculated by using the equation: mass = force / acceleration. In this case, the force would be the weight of the car and the acceleration would be the constant speed at which the car is traveling on the bridge. The mass can also be calculated by measuring the gravitational force acting on the car and dividing it by the acceleration due to gravity.

## 2. Why is it important to calculate the mass of a car on a bridge?

Calculating the mass of a car on a bridge is important because it helps engineers and scientists understand the structural integrity of the bridge. By knowing the mass of the car, they can determine if the bridge can safely support the weight of the car without collapsing or causing damage.

## 3. What factors can affect the mass of a car on a bridge?

The mass of a car on a bridge can be affected by various factors such as the weight of the car, the weight distribution of the car, the speed at which the car is traveling, and the condition of the bridge. Other factors such as the type of road surface and weather conditions can also impact the mass of the car on the bridge.

## 4. How does the mass of a car on a bridge affect the bridge's stability?

The mass of a car on a bridge can significantly impact the bridge's stability. If the bridge is designed to support a certain weight limit and the mass of the car exceeds that limit, it can cause the bridge to become unstable and potentially collapse. Additionally, the distribution of the car's weight can also affect the stability of the bridge.

## 5. Can the mass of a car on a bridge change while it is in motion?

Yes, the mass of a car on a bridge can change while it is in motion. This is because the car's weight and weight distribution can change as passengers exit or enter the car, or as cargo is loaded or unloaded. Changes in speed and acceleration can also affect the car's mass as it travels on the bridge. It is important to consider these changes in order to accurately calculate the mass of the car on the bridge.

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