Question

You apply a 75-N force to pull a child's wagon across the floor at a constant speed of 0.5 m/s. If you increase your pull to 90 N ,the wagon will

• A. continue to move at 0.5 m/s.
• B. speed up immediately and then move at the faster constant speed of 0.6 m/s
• C. speed up gradually until it reaches the speed of 0.6 m/s and then move at that constant speed.
• D. continue to speed up as long as you keep pulling.
• E. none of the above

Answer 1

The correct option is B speed up immediately and then move at the faster constant speed of 0.6 m/s

Given force $F_1=75N$ and velocity $v_1=0.5m/s$

we know force= mass$\times$ acceleration

also acceleration $a=\frac{v-u}{t}$ where v=final velocity and u= initial velocity

Thus $F_1=m\left(\frac{v_1-0}{t}\right)$ considering initial velocity to be 0 m/s as initial it is at rest

$\frac{m}{t}=\frac{75}{0.5}=150$

Similarly when the wagon is pulled by a force 90 N its velocity will be

$v_2=\frac{Ft}{m}=\frac{90}{150}=0.6m/s$

As mass will be same as the same wagon is used in both the cases , and assuming time to same.