What Forces Affect a Cyclist Coasting and Climbing a Slope?

[Min_Shin]

A man of mass 85kg, on a bicycle of mass 15kg, coasts down a slope inclined at 4.5* to the horizontal, at a constant speed of 4.7m/s.
a)what is the force of friction on the man and his bicycle?
b)if the man wanted to ride up the same slope at the same speed, what force would he have to exert?
c)if the man exerted a force of 150N up the hill, at what rate would he accelerate?

a)I thought the force of friction would be equal to the sine angle componenet of the force of gravity on the mass. 100g*sin 4.5* = 77N

b) Since going up the hill, i thought he needs a force that could counterbalance both slide force of the mass and friction force (since the movement is up the hill now), so i doubled the magnitude of the friction force i got at a) 77N * 2 = 154N

c) But now i was wondering if he only exerts 150 N up he wouldn't even be able to climb the hill.. which i don't think is the answer to the question

Where did i go wrong?

btw thanks in advance!

 

[OlderDan]

I assume part c) is the only thing bothering you. Suppose the man starts up the hill with some velocity. You can still calculate an acceleration. He might even make it to the top of the hill.