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    emilyfreeman96's Avatar
    emilyfreeman96 Posts: 3, Reputation: 1
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    #1

    Mar 27, 2012, 12:14 PM
    Anyone good at GCSE Physics?
    Hello,
    I really need help on this physics homework that I received today which is about force, mass and acceleration (GCSE level).I would really appreciate if someone could help me.

    1.a) The motorcyclist is moving at a constant speed of 20m/s. The value of the driving force is 2000N. What is the resistance force?

    B) The motorcyclist increases her speed from 20m/s to 30m/s in 5 seconds. Calculate the acceleration of the motorcyclist.

    C) Calculate the force needed to produce this acceleration.

    D) What is the total force produced by the bike during this acceleration?

    2.a) A car is moving at a constant speed of 30m/s. The mass of the car and the driver is 1000kg. If the driving force is 3000N, what is the value of the resistive force?

    B)If the driver presses the accelerator and increases the driving force to 4000N, calculate the acceleration of the car.

    3. A car decelerates from 15m/s to a standstill in 5 seconds. The mass of the car and driver is 1000kg. Explain how the force required to produce the same deceleration would change if the mass of the car and driver was increased to 1500kg.

    I have tried to do it, but I am really not confident with it.
    Thank you :)
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Mar 27, 2012, 12:21 PM
    Please show us what you have tried, and we'll help you along. For example - the first problem involves a motorcycle that is not accelerating, so the sum of forces on it must be 0. Can you figure out the resistive force given that the driving force is 2000N?
    emilyfreeman96's Avatar
    emilyfreeman96 Posts: 3, Reputation: 1
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    #3

    Mar 27, 2012, 12:33 PM
    Sorry, I forgot to add some information for the first question: the total mass of the motorcyclist and motorcycle is 250kg.

    I then used the formula:
    Force (N) = Mass (kg) x Acceleration (m/s^2)
    So I did 2000N / 250kg = 8
    But I'm not sure that gives me the resistive force...
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #4

    Mar 27, 2012, 01:09 PM
    From you know that if a = 0 (because the motorcycle is moving at a constant speed) then . There are two forces acting on the motorcycle: 2000N trying to make it go and a resistive force trying to make it stop. Since these two forces cancel out, what must be the value of the resistive force?

    Please show us what you've attempted to solve the other questions and we'll be glad to help you out.
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