6. Sarah and her bicycle have a total mass of 40 kg. Her speed at the top of a 10 m high and 100 m long hill is 5 m/s. If the force of friction on her way down is 20 N, at what speed will she be going when she reaches the bottom?

a. 5 m/s
b. 10 m/s
c. 11 m/s
d. She stops before she reaches the bottom

Question

6. Sarah and her bicycle have a total mass of 40 kg. Her speed at the top of a 10 m high and 100 m long hill is 5 m/s. If the force of friction on her way down is 20 N, at what speed will she be going when she reaches the bottom? 
 
a. 5 m/s 
b. 10 m/s 
c. 11 m/s 
d. She stops before she reaches the bottom

anonymous · Answer

First we need to figure out forces acting on the girl. Drawing a free body diagram is a good  way:|dw:1392002436328:dw|

Now we need to figure out what part of her weight is pulling her down the slope. If the she were in free fall and the angle was 90deg, how much of her weight would be accelerating her?