A ball of mass 2kg travelling in a straight line at 4ms^-1 is acted on by a force of 3N acting in the direction of motion for 5 seconds. What is the speed of the ball after 5 seconds?
vf=vi+at but a=force/mass
a = 3÷2= 1.5
vf=4+1.5×5=
vf=4+7.5
vf=11.5m/s^-1
Is this correct? If not please can you correct it for me
That is correct assuming that the ball is sliding, not rolling. If rolling there is a force back on the bottom of the ball to give it angular acceleration but I suspect you have not covered that. Let's just assume that is a net force of 3 N :) In other words the 3 N is the forward force minus the backward force.
vf = 11.5 m/s or 11.5 ms^-1
but not m/s^-1 = m/(1/s) = ms
You have correctly identified the formula to use, vf = vi + at, where vf is the final velocity, vi is the initial velocity, a is the acceleration, and t is the time.
To calculate the acceleration, you correctly used the formula a = force/mass. Given that the force acting on the ball is 3N and the mass of the ball is 2kg, you correctly calculated the acceleration as 3N / 2kg = 1.5m/s^2.
Next, you substituted the values into the formula and calculated the final velocity: vf = 4 m/s + (1.5 m/s^2) * 5 s = 4 m/s + 7.5 m/s = 11.5 m/s.
Therefore, your calculation is correct. The speed of the ball after 5 seconds is 11.5 m/s. Well done!