Math Is Fun Forum

1. If a force is applied to a 2kg mass, which is initially at rest on the frictionless surface, for 3 seconds and then removed, what is the speed of the object after 6 seconds?

Do I have to just calculate for the first 3 seconds? For the remaining 3 seconds does the speed remain constant?

2. The brakes of a 1.2 tonne car exert a stopping force of 2500 N. How long would it take the car to stop if the brakes were applied when the car was travelling at 15 ms-¹.

My working:

Ok, I think that's correct, but... I have a question:
1. If the friction is 0, will the car even be able to break?
2. If the answer to 1. is no, then what is the correct level of friction that will result in a stopping time of 7.2s?

3. A trolley pulled down a friction-compensated slope by a cerain force has an acceleration of 1 ms-². When the mass of the trolley is doubled and the pulling force trebled, what is the new acceleration, assuming that an adjustment is made to friction-compensate the slope again?

Thanks, I have a physics test on monday and I want to clear up a few things