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Car with mass of 1500kg and thrust of 4000N

  • Thread starter jtwitty
  • Start date
  • #1
35
0
Sorry; this is like soooooooo hard

Homework Statement



A car with a mass of 1500 kg has en engine which can produce 4000N of thrust. Assume that the air resistance on the car is a constant 500N. If the car starts from rest, how fast will it be moving after 10 seconds.

Homework Equations



d=1/2at2+vit
a=f/m


The Attempt at a Solution



a = 4000 / 15000
a = .2666666666666666666666666666666666666666666666666666666666
thats about as far as i can get cuz that a has to be wrong?
 

Answers and Replies

  • #2
35
0
heres what i just came up with

netforce = 4000 - 500 = 3500

a = 3500/1500
a = 2.4

d= 1/2a(100)
d=120m

a = vf /t
vf = 24

????????????
 
  • #3
380
1
First you need to determine what the NET force will be on the car. In this case you have 4000N of thrust in the positive x direction (indicate as 'right' on your free body diagram), you also have a 500N resistive force due to air drag (left).

Your net force will be 4000N-500N (3500N).

Since [itex] F = ma [/itex], [itex] a = \frac{F}{m} = \frac{3500}{1500} = 2.33333 [/itex]

Remember to look at the units of the values you are given. For some reason you added another 0 to your mass, which is why you got that strange value for a.

From that value of a you should be able to determine the velocity now after 10 seconds, use constant acceleration forumlae.

Edit - ninja'd.

Edit2 - One small correction to your answer. Since 3500/1500 = 2.33333333, rounding up to 2.4 is incorrect. 2.3 would be the appropriate value if significant figures aren't important for this problem. Thus your final answer would be 23m/s
 
  • #4
35
0
haha :)))

thanks so much man :)
 

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