Physics Multiple Choice help?

Question

1. A sled of mass 40.0 kg is pulled along flat snow covered ground. the static friction coefficient is 0.28 and the sliding friction coefficient is 0.08. what force will be needed to start the sled moving? 
           A. 147 N      B. 31 N       C. 110 N          D. 392 N

2. A net force gives a 100 kg object an acceleration of 2.0 m/s^2, what acceleration would the net force give a 200 kg object? (answers in m/s^2)
         A.  0.5    B.  4.0    C.  1.0    D.   5.0 

3. On Earth a scale shows you weigh 490 N. what is your mass?
        A. 50 kg   B. 22 kg        C. 100 kg       D. 75 kg

Fireman · Accepted Answer

1) By F(applied) ≥F(static friction) for motion:-
=>F(minimum for motion) = Ff = µs x N = µs x mg = 0.28 x 40 x 9.8 = 109.76 N =>(C)
2) By F = ma
=>F = 100 x 2 = 200 N
Again by F = ma
=>200 = 200a
=>a = 1 m/s^2=>(C)
3) By W = mg
=>m = W/g = 490/9.8 = 50 kg=>(A)

Physics Multiple Choice help?

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