# A forces and motion AS question.

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#1
This question is from set 2 paper 1 of the AQA AS physics specimen materials:

A car is designed to break the land speed record. The thrust exerted on the car is 230 kN at one instant of its motion. The mass of the car at this instant is 11 000 kg.
The acceleration of the car at this instant is 2.9 m s–2 .
Calculate the air resistance acting on the car.

I would have calculated the resultant force from acceleration * mass, and taken this away from the thrust, which would have given me 198100N, but this is not correct according to the mark scheme.

The mark scheme says:

resultant force = 245 000 × 2.9 = 710 500 (N)
resultant force = thrust – weight – air resistance 710 500 = (3200 × 103 – 245 × 103 ) × 9.81 – air resistance
air resistance = (3200 × 103 – 245 × 103 ) × 9.81 – 710 500 = 86 000 (N)

I don't understand where the 245000 comes from on the first line of the MS, or where the weight comes into it. Am I missing a formula or something?
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2 years ago
#2
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#3
I suspect it's a bogus question, but it's from AQA's official specimen material, so I'm not sure.
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2 years ago
#4
(Original post by 178865)
This question is from set 2 paper 1 of the AQA AS physics specimen materials:

A car is designed to break the land speed record. The thrust exerted on the car is 230 kN at one instant of its motion. The mass of the car at this instant is 11 000 kg.
The acceleration of the car at this instant is 2.9 m s–2 .
Calculate the air resistance acting on the car.

I would have calculated the resultant force from acceleration * mass, and taken this away from the thrust, which would have given me 198100N, but this is not correct according to the mark scheme.

The mark scheme says:

resultant force = 245 000 × 2.9 = 710 500 (N)
resultant force = thrust – weight – air resistance 710 500 = (3200 × 103 – 245 × 103 ) × 9.81 – air resistance
air resistance = (3200 × 103 – 245 × 103 ) × 9.81 – 710 500 = 86 000 (N)

I don't understand where the 245000 comes from on the first line of the MS, or where the weight comes into it. Am I missing a formula or something?
No, your working is right. Thats the thing with these specimen papers some of the answers are wrong.
0
2 years ago
#5
(Original post by 178865)
This question is from set 2 paper 1 of the AQA AS physics specimen materials:

A car is designed to break the land speed record. The thrust exerted on the car is 230 kN at one instant of its motion. The mass of the car at this instant is 11 000 kg.
The acceleration of the car at this instant is 2.9 m s–2 .
Calculate the air resistance acting on the car.

I would have calculated the resultant force from acceleration * mass, and taken this away from the thrust, which would have given me 198100N, but this is not correct according to the mark scheme.

The mark scheme says:

resultant force = 245 000 × 2.9 = 710 500 (N)
resultant force = thrust – weight – air resistance 710 500 = (3200 × 103 – 245 × 103 ) × 9.81 – air resistance
air resistance = (3200 × 103 – 245 × 103 ) × 9.81 – 710 500 = 86 000 (N)

I don't understand where the 245000 comes from on the first line of the MS, or where the weight comes into it. Am I missing a formula or something?
Someone in the forum actually commented it is about a rocket NOT car problem for this set of paper. You can find the comment here.
https://www.thestudentroom.co.uk/sho...3968699&page=4
1
#6
Thank you everyone.
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