Answer to Question #217241 in Physics for Rethabile

Question

A car starts from rest and accelerates uniformly at a rate of 2 m.s-2 for 20 s. It then maintains a constant velocity for 10 s. The brakes are then applied, and the car is uniformly decelerating and comes to rest in 5 s. What is the maximum velocity and the deceleration in the last 5 seconds?

Question 1 options:

a) 

20 m/s and 4 m/s².

b) 

10 m/s and 2 m/s².

c) 

No option is correct.

d) 

30 m/s and 6m/s².

e) 

40 m/s and 8 m/s².

Answer 1

The maximum velocity

$$v_2=v_1+at_1=0+2*20=40\:\rm m/s$$

The deceleration

$$a_3=\frac{v_3-v_2}{\Delta t_3}=\frac{0-40}{5}=-8\:\rm m/s^2$$

Answer: e)